It won’t be a break for you with in-laws if you don’t get on great. They will simply insist on doing everything together and you won’t get a proper break, or the family time you want.
If you want to include them, do a 3 night stay in the uk. See how it goes. Just be prepared to do everything with them and let them take over etc.
Holidays with kids are difficult. If they are young and need naps, you’ll know from experience it’s just a lot of waiting out the afternoon in a small hotel room. My suggestion would be a euro camp style holiday or apartment. Go self catering. That way, you can eat when it suits you, sit on a balcony whilst the kids nap. There will be more space. French campsites are awesome. Places like centre parcs are too. You want space and alone time, so sack off fancy hotels.
Plus, if you do take the in-laws, they would have to stay in a separate static home or similar, so much better for keeping distance.
Pick a place with a pool and on-site restaurant etc. Much more fun that way, as there’s room for the kids to run about, your own room and lots of on-site activities. Having an extra pair of eyes on the kids by the pool is handy, but you won’t be free to relax.
Do you have siblings? Might be more fun to go with people your own age.
I’ve been away with my parents, and with the in-laws. Great to have the memories for the kids, but I did feel a bit claustrophobic from having to do things together all the time, and I think we only had one night off! It was a bit testing at times, but I would do it again.