The FIL issue sounds fairly common. A lot of guys rough around, too hard; some men just come from backgrounds that make them think this is standard, the boys they rough house with need to "toughen up". My ex boyfriend was like that. It was something we frequently argued about and did ultimately put strain on our relationship. He thought it was perfectly normal, but my son would tell me "He's too rough". I knew that my ex didn't mean to be that way, it was just the way he was, but anytime I addressed it he would feel like I was picking on him and just didn't want my son to play because God forbid he get roughed up a little. Just like the other M. said, I refereed quite a bit. They would horse around, but when they got to crazy I put a stop to it and quickly, usually just by raising my voice "ENOUGH guys, knock it off". If FIL wants to argue with you afterwards, look him in the eye and tell him he doesn't have to agree with you, its not up to him, but he WILL respect you (and if he can't do that, you can leave). I have a natural edge to my personality, and most anyone who knows me knows if I say something like that I've had it and not to cross me.
The MIL thing, I worry about the same thing with my M.. She is very elusive about her finances though, all I know is that she spends money and a lot of it, and I know she can't have that much to begin with. She has always had bad spending habits and when married to my dad almost drove him into bankruptcy, she herself has filed before about 10 years ago. However, I have always been taught that other peoples finances are absolutely none of my business, and it is not in my rightful place to say anything. Think of how you would feel if your kids were constantly telling you that you mishandle your finances; even out of concern, it can cause resentment. Its just not their place. And think of this too; a lot of women/people shop like that, literal "shopaholics" because they are lacking something in their lives and feel the need to fill a void. Maybe you should look less at her spending habits and more at where she spends her time. Is she lonely? Is she maybe trying to buy your kids love (even though they of course already love grandma plenty)? Maybe if you spent some extra time with her every week, instead of going to the mall maybe go to the movies with her, maybe just a walk through the park, some free activities, or even a pottery or a sewing class together, might really help her.
To be concerned is human, to want to help is human, but to involve yourself by directly putting her ability to control spending "on blast" is imposing. If you don't want the kids to have the gifts, see to it you get to the gifts first and either give them back to grandma or tell her they are going to charity. If she starts to sneak behind your back, you might want to go as far as taking the gifts away from the children after they have gotten them. Be honest with them "Mommy told grandma no presents this time, I'm sorry but you can't keep them". Could serve as a dose of reality for grandma and the kids. Grandma can't sneak and the kids know mommy means business and what you say absolutely is gospel in your house. Hard core but I bet you if you did that once or twice, grandma might just quit.
Good luck