I've had to tell my mother in law, sisters in law and mom all to fuck off at one point or another.
The thing that pisses me off is when someone pulls my kid away from me because I'm doing something wrong or just differently than they would. I don't like that under ANY circumstances, in fact it's one of very few things that will get me legitimately boiling.
So after it happened a couple times, I told the entire family as a group that it doesn't happen anymore. I acknowledged that I will be ignorant about certain things and might even, worst case, put the kid at risk of a mild injury. (like bending his knee in a funky way when putting him in a bouncer or jerking his elbow a little too much when putting it in a shirt). But if that's the case, I want to be told what I'm doing wrong and explained a different way of doing it.
Hasn't happened since and people have been very respectful about that boundary.
I think the key is that hopefully you're lucky enough to be surrounded by people, who when they are annoying, are annoying because they care and are trying to be helpful. Passive aggressiveness is a big time peeve of mine. That's when I'd usually recommend calling the person out, "You're being passive aggressive right now which tells me there's something more serious that you want to get off your chest with me that you're not saying. Please tell me what you're upset about now so this doesn't get worse over time."
I've done that with my wife on multiple ocassions and it's worked fantastically. It's disarming and it's really the only possible win against passive aggressiveness. the hope is it will force the person to either go into full meltdown mode (which you couldn't have prevented in the first place) or it shocks them into helping you both out and saying what's up. Then you can work through the problem with whomever it is and get back to being a team. That can be done with a mother in law as well, unless she's nuts. In which case...your wife is probably nuts too.
I'm lucky in that my wife is far more rational than 99% of women, so when she's being irrational if it's pointed out to her she'll back off of it. If not immediately, then within a few minutes or so. Not everyone is that lucky, so I guess for others you may just have to tolerate it.
So yeah...passive aggressiveness will come up.
And it will likely come up when there's something that creates as much emotion in as many people as a baby does.