Side trip from Paris to Bruges or Ghent? Or both?

It is possible on one day: the hourly high-speed Thalys train service brings you from Paris in 1,5 hrs to Brussels, where you change for a train to Gent (30 mins) or Brugge (an extra 30 mins on the same train). It does mean 5 or 6 hrs on the train for a short visit. Better is to stay one night which gives much more time to explore and enjoy both cities. (Some would advise you to have Gent for that, others Brugge.) And English is widely spoken.

Ghent or Bruges? Or both? Could we hit up both in one day or would it
be worth it for us to do an overnight and dedicate a day to each?

That's what I would do. They're both well worth an entire day, and trying to do both as a day trip from Paris would eat up too much time in transport.

Yeah I think we will spend the night in one of the cities. Would it make sense to go straight to Bruges spend the night and then next morning head to Ghent and spend the whole day there before heading back to Brussels to catch a train to Paris?

What are your favorite things in these places that if you only had 1 day you would for sure do?

I would spend a night in Brugge (local spelling, in Flemish). You would be to rushed trying to do it as a day trip from Paris.

Also.. do they speak English there?

No, they speak Flemish. But most people who work in the tourist trade will speak enough French and English to talk to you. Probably more English than in Paris.

Thank you Chris F.

I am trying to learn french( I am terrible) but maybe I can try and learn some basic phrases in Flemish to help us get by?

We are very excited as this is our first trip to Europe.

A practical thing: when sightseeing Gent between Brugge and Brussel you don't want to carry your overnight things. It's good to know that the Gent railway station (you need Gent-Sint Pieters) has lockers.

Also.. do they speak English there?

Yes. Very well, as a rule. We had no issues at all with language, not to say that you might not run into someone who is not multilingual.

What are your favorite things in these places that if you only had 1
day you would for sure do?

Up to you. As your time is short, I'd highly recommend spending to some time with some guidebooks to choose what you find most interesting to YOU. We had a lot more time in Bruges than you will so didn't need to be quite as selective.

No need to learn Flemish. It is not an easy language to learn unless you know Dutch, still a different language. Most people speak English. We spent weeks in Brugge last spring without knowing any Flemish. People are very nice and friendly.

In my experience, most people you will meet in Dutch-speaking cities in Belgium will speak English and will strongly prefer it to speaking French, for local political reasons.

In addition to guidebooks, the tourism websites for Bruges and Gent should be helpful when choosing things to do:

https://www.visitbruges.be/en
(It's sometime a little slow/glitchy so be patient if it's acting up.)

https://visit.gent.be/en/home