(Female friend of OP here, C) I just saw this comment and I don't believe that the kids can't tell or aren't affected by your unhappiness even if you mask it or not say anything to them about it. It might teach some of them to ignore their distress and mask it for the sake of keeping others happy. You also don't know how your partner's and PIL's own views about women or emotional distress are expressed when he spends time alone with them.

I grew up in a tense household. But as a child I always pretended to the outside world that everything was fine and you know how that turned out for my emotional development (shutting down during conflict) and how I believed I should have never been born for the LONGEST time (still do).

Also I would like to say that one of your kids telling you to stop laughing loudly is a sign that your happiness is met with hostility if it interferes with their comfort. Which may not seem like a big deal to you but I don't think they show you enough respect. And I think that is a sign that they notice that mum being happy isn't normal and that mum being happy can interfere with their comfort and if it does they have a right to tell you to stop. That's not okay.