North Wales with our 4 (Dutch) chidren/teens - where to stay and what to see please

Have your children said what they might like to see/visit?
North Wales is a very popular tourist destination with lots to do, some that doesn’t involve walking! :-)
Lots of suggestions here
https://www.visitwales.com/

If the weather is OK taking the train up Mount Snowdon would be fun. (The English names of Mount Snowdon and wider Snowdonia have officially been replaced by their welsh names, Snowdon is now known as Yr Wyddfa and Snowdonia is Eryri, but the English names are still commonly used.)
https://snowdonrailway.co.uk/

For something more active look at Zip World. My teenage nephews loved it.
https://www.zipworld.co.uk/

Conwy is a nice place to do but it is a small town, with not that many shops of interest to teenagers.
A mile or so down the coast you will find Llandudno, a Victorian holiday resort with more to do.

If you haven’t already, have a look at Chester, between Liverpool and Wales. A really historic and pretty town with lots to do for all ages.

https://chester.com/

As Emma says, Conwy (walled medieval town with a ruined castle) or Llandudno (Victorian seaside town) would work well. But it would be helpful to know what the kids are specifically interested in (apart from no walks and near shops...) as it might be there would be better places to stop - like Criccieth another seaside town with a ruined castle which gives acess to Portmeirion as well as the Ffestiniog and Welsh Highland preserved steam railways. Conwy area can be done as a day trip from there as well as Caernarfon and Harlech Castles.

With 4 teens and 3 days, I’d choose the larger Llandudno. To me, Conwy is pretty small.

Teens/children who don’t want to hike - hmm ... Are they looking at screens all the time? Holidays are for encountering new experiences and being away from normal day to day life.

If in north Wales, just west of Conwy is a village called Abergwyngreggan from where a small road goes a short distance to a car park for the 1 hour hike up to ABER FALLS. If you click this link, you can see a You Tuber describing the walk and showing the falls. I suggest you show it to your children and say that by not walking on trails, that they miss out on so much. Hopefully, you will take them on the hike to this waterfall and when they have got all their photos to send to friends, they will realise that doing such walks is worthwhile and also good for their health.

Bodnant Gardens (NT) are also well worth a visit when in north Wales.

When going from N Wales to the Cotswolds, suggest you travel on the A470 south through Wales as far as Rhayader and then take A44 east to the Cotswolds.

The small town of Leominster is on the A44 and worth a quick look. The A44 then goes to Bromyard and I highly recommend a stop at > https://www.nationaltrust.org.uk/visit/worcestershire-herefordshire/brockhampton/things-to-see-at-brockhampton-manor-house

I would also agree with the suggestion to look at Llandudno over Conwy and would also suggest looking at Caernarfon especially if they are interested in castles. From Caernarfon it's also very easy to get over to Anglesey which has another castle (Beaumaris).

My sister and I were in Wales in August. She isn't much of a walker, either. I would stay in Llandudno. There's more to do. We took the Great Orme Tram up to see the Great Orme. Those who want to walk, can walk around up there and others can sit and have coffee or a snack. There's a pier with amusements in Llandudno, and there are several beaches. On a couple mornings, I would get up early and walk the hills while my sister was waking up. Conwy is very close and we took the bus to Conwy to see the castle and Plas Mawr. We then went to Caernarfon and saw the castle and spent a couple nights there. From Caernarfon, we took the public bus to Betws-Y-Coed and had lunch and looked at shops. The bus ride was very scenic. All these things are very close, so you could base in one place. And I'd recommend Llandudno for the base, especially if you have a car.

Thank you all for your suggestions. Much appreciated.