London without top sightseeing destinations

I recommend some structure to your limited time. At least visit Westminster Abbey and the Churchill War Rooms which are adjacent to each other.
Then get out and explore.

I think you’ll want to see some of the landmarks. Go to the Thames and see Big Ben and walk along from there to Tower Bridge. You can divert to see places on that general route, eg Covent Garden, St Paul’s. You don’t have to follow the river exactly. I would have no problem with not going inside places. You need a lot of time to make a visit worthwhile.

The Sky Garden is at the end of this basic route and offers amazing views for free. I think that would be worth doing. You could even start there.

I loved just rambling around Hampstead Heath park.

If you or your kids are Ted Lasso fans, you can take the tube to Richmond.

What do your young adults want?

If they haven't been before, maybe a self-directed walking tour past the sites unique to London? If you prefer guided tours, London Walks has different focuses and generally very good reviews. Thames River trips from a number of companies if walking isn't a pleasure..

https://freetoursbyfoot.com/self-guided-walking-tour-london/
https://www.walklondon.com
https://www.city-walks.info/London-en/Walks.html

Probably very few would find this appealing, but my then younger adult and I explored Canary Wharf for half a day. "Kid" wanted to compare with the financial area of the Asian city where then living and working. "Cool" for us - probably not for many. It's hard to know what you/they might enjoy without more info.

Take at least one walk with the London Walks company:
https://www.walks.com/

Guided walks through historic neighborhoods. There's even a Beatles walk.
We're all big fans of this company on this forum.

Take a riverboat ride on the Thames Clipper/Uber boats.
Just tap in with your Oyster card when you get on, tap out when you get off.
Or use a contactless credit card or Apple watch.
Here's a map of the route including docks along the river where you can get on and off:
https://www.thamesclippers.com/plan-your-journey/route-map

Consider a boat ride to Greenwich just to walk around.
You could leave from the Westminster area or from the pier right behind the Tower of London.
You really get a great view of London from the water.

Thank you for the ideas.
We are all big Ted Lasso fans so Richmond might be fun!
My son is a big soccer fan and my daughter loves books.
We originally wanted to go up to Manchester to see a Man City game but couldn’t get tickets.

Greenwich is a nice day out and is easily reached by boat or tube. However, if you have not been to London before, then why skip the best sites? They are fairly close together and all have easy connections. The Tower and Tower Bridge can be easily reached by the Uber boats from Westminster (by the London Eye). In the other direction, walk past Big Ben and Westminster Abbey, go through St. James Park and there you are outside Buckingham Palace. Walk down the Mall, through Horse Guards Parade, and you are outside Downing Street. The young adults might enjoy China Town and Covent Garden. I plan to do all of this for the young bridal party that is coming to England for my daughter's June wedding. None have been to England before and are so excited to see the big sites of London.

My 25 year old daughter was in London this time last year and loved the Covent Garden/Soho area just to wander in the evening. She also loved doing a Jack the Ripper tour.

I can definitely see the appeal of skipping the big sightseeing destinations. I've lived in London since 2009 and I've never been inside Westminster Abbey or ridden the London Eye.

When is it you are in London? I've got a couple of suggestions that work best in the summer.

If you're after neighbourhood experiences, you could think about a trip to Peckham. It's gentrified quite a bit but it's still quite rough around the edges. A couple of Peckham destinations could be Frank's or The Bussey Building. Frank's is a bar / restaurant on the rooftop storey of a parking garage. It's run in the summer months by art collective, Bold Tendencies. I'm not sure what's planned for this year, but there's usually some art installations curated by them in the lower floors. The views of The City from Frank's are great, especially on a nice summer evening at sunset. It opens May 17th. The Bussey Building is a creative space almost next door which also has a rooftop bar. A walk around Peckham Rye lets you see a side of London most visitors miss.

Somewhere else that's good on a weekend if the weather is nice is Hackney Wick. There's some decent walking along the canal and several places one may stop for refreshments. The most iconic place might be The Lord Napier, near Hackney Wick Overground station. It is an old pub which ended up being squatted for many years, before falling into dereliction, and then reopening some years ago.

Staying in Hackney, London Fields is a good spot on a nice day. It gets busy on summer weekends with people hanging out. Saturday is when the nearby Broadway Market is best. It's a short walk down the Regents Canal to Victoria Park or a good hike in the other direction to Camden.

There's quite a bit to experience in Dalston, also in Hackney. Maybe my favourite restaurant in all of London, Mangal II, is a short walk from Dalston Kingsland or Dalston Junction stations. There's Ridley Road Market, mainly produce but with some take out food. Kingsland Road all the way up to Stoke Newington is good to wander on a weekend. It's a good place to seek out live music, there's a few small venues. The Shacklewell Arms has music almost every night. I like Cafe OTO, for the more experimental side of things.

Pub crawl including many older pubs in downtown. I also second the ramble in Hampstead Heath.But it would be a shame to not see some of the highlights of London.

My son is a big soccer fan and my daughter loves books.
We originally wanted to go up to Manchester to see a Man City game but couldn’t get tickets.

I didn't notice your post when I made my last post about some neighborhoods to see.

As far as books go, the big bookstores are in central London mainly. Some that spring to mind are Hatchards in Piccadilly, Waterstones, also in Piccadilly, and Foyles on Charing Cross Road. Daunt Books has a number of branches; any in London are going to make a good destination for seeing a different neighbourhood.

There's a daily secondhand book market on The Southbank, by The BFI.

As I mentioned Hackney above, I'd mention Pages of Hackney, my local independant. A fairly small but expertly curated selection of new books, with used in the basement.

I also mentioned Broadway Market and that is home to The Broadway Bookshop and Donlon's. Donlon's specialises in art books and I've been drawn in to browse by their window display a couple of times. There will also be secondhand books on the market on a Saturday.

I mentioned Dalston and Stoke Newington too, Stoke Newington Bookshop is another cool little independant in that area. 100 yards up the road is Abney Park Cemetery, where the video for Amy Winehouse's Back To Black was shot. A lovely little spooky Victorian cemetery.

I only mentioned Camden in passing in my last post, but for used book shopping as a destination, that would also allow you to experience the delights of Camden Town, I'd recommend Walden Books.

As far as football goes, the consensus on here seems to be to forget about seeing Premier League teams unless you're willing to deal with what are essentially touts or exorbitant hospitality packages. Tickets for teams that play in the lower leagues still offer good football and enthusiastic crowds. Leyton Orient or Millwall might be options if you're in town before the season ends or for the new season.

We are all big Ted Lasso fans so Richmond might be fun!

I'm still in England now but spent an afternoon in Richmond back in late March. I ate a late lunch at The Prince's Head, which was the Crown and Anchor pub on the show, strolled through Richmond Green (the park Ted walked through), saw his "apartment" (11a Paved Ct - right up the street from the pub) and then took a walk along the Thames (which is much narrower here). It was a lovely afternoon and I really enjoyed it.

If you're interested in filming landmarks, here's a good site: https://people.com/travel/ted-lasso-locations-london-richmond-real-pub-stadium-where-filmed/