While the advice to not parent is somewhat sound? At the same time you need to be an adult...and that means if kids are acting like village idiots at some point, you feel free to tell them to STOP IT.
Granted, they may not push your buttons, may not be that type of kid, but too many get in habit of "I want to be a friend and will let dad/mom correct and I won't say anything when they break my TV" BS.
If you would tell neighbor kids or kid relatives something, then don't hold back with this situation.
And always keep in mind that what kids might tell you, might be the truth, twisted around, or an outright lie too. The "young/pretty" deal? Might have been nothing more than kids saying "I don't think she is pretty" or "I think she is really pretty" and Mom being preoccupied with something, or joking and saying "are you saying she is prettier than ME???" and cutting up too.
My youngest married a man with 4 kids....the 2 middle are twins he had out of wedlock with couple of night stands with a druggie/thug/drunk....boy twin is messed up because of her, and mean seriously too. The oldest son and the youngest girl are the legitimate kids by his wife...(why she didn't shoot him I don't know) but when they get them, it is all 4 at once.
And it has been pretty problematic too. Kids feel free to ask daughter "are you ever going to get out of college?" And loads of personal questions that in no way, shape or form would I allow. Daughter was waiting for their dad to say something....told her to look them dead in the eye and tell them GROWNUP BUSINESS! And then tell them to go find something to do.
And you need to meet Mom, as if kids know the 3 (or 4 if she has married) are on same page, the kids can't play the two sets of adults against each other.
Remember too, that when the kids are toting you a bone, they are taking one away. So watch what you say.
You do not have to be a parent per se...BUT you are an adult and should expect to be treated as such, setting those ground rules in advance will help down the road.
I've had one good WIL...or wife in law, as we called each other....but the rest? Were POS.
I've been a stepmom and had steps as a kid, and have had steps for my kids too.
Mostly it doesn't work out. But it can....if you have good sense, and stand your ground, and keep in close contact with WIL on matters pertaining to kids.
This can be a wonderful opportunity for the kids to have several adults in their life that are behind them.
The best of luck to you and all of them. I think you will do splendidly.
Horses make me a better person.