Mid 60’s MIL hinting that she wants to breastfeed my baby, how weird is that???

As of right now I am staying with my in-laws until my baby arrives because the hospital is closer to their house. A family friend of theirs with a 6 yr old autistic boy also lives next door, and I found out recently that my MIL breastfed this child when he was young. Even though he’s 6 now, I still see him running up to my MIL and sucking on her tits over her shirt like it’s just normal behavior. I pointed it out to my MIL saying it’s weird and that he’s old enough to learn that it isn’t okay to do that anymore, but she said it’s fine because she breastfed him and also my husbands nephew (who is now 5). The mother of the boy just standing sheepishly to the side with an awkward smile on her face like nothing is wrong. She then joked to my husband saying that my baby (who will be arriving in the next two weeks) might like her milk too. My husband said “hell no” immediately, and now I’m just beyond weirded out and even mildly grossed out but I have no idea if anyone else has experienced this before. What do I say in a situation like this? Now I’m hesitant to leave my baby with my MIL in case I walk in on her mid-feed. I think I would simply ✨lose my shit✨

Edit: wowow, so many comments in a short amount of time! Thanks for your input and opinions, although some are emotionally driven. I want to respond to certain questions/comments to clear the air.

1) The neighbor/mother of the autistic child and my MIL are supposedly “best friends”. I don’t know the extent of their relationship and I don’t ask because it’s not my business, but I guess they had a mutual understanding because she literally does not care that her son still reenacts nursing on my MIL at this age. I’ll also add that the neighbor enables her child to do inappropriate things to other women around him, myself included; he will walk up behind me and spread my buttcheeks and shove his face in it, grab my tits and also shove his face into my very pregnant belly. I always push him away and tell him to stop but his mom doesn’t react unless she sees me react. I get that he has a mental disability and his level of autism is supposedly at the most severe, but surely you can still teach your child to respect boundaries and to not do certain things?

2) I love my MIL and she’s great for the most part but has a tendency to be over-dramatic and controlling when it comes to certain things. Pregnancy is definitely one of those things. She has been trying to control what I eat, my water intake, where I travel to, what to buy for baby, I could literally name a thousand more things but I’m sure you all get it. In my husband’s family, she is known to be the children’s caretaker. (We are Southeast Asian, so there is cultural influence, however my husband and my sister in law were born and raised in the US.) She has had 3 children of her own and has taken care of both of her grandkids (my son will be her third). Basically she is an expert at raising babies and is expected to help in the first year or so with my son, especially since I am a FTM. So I get it that she might want to give me plenty of advice but she does go overboard and it’s irritating and overwhelming. Her intentions are good but the delivery is meh.

3) My husband had no idea that his mom was breastfeeding his nephew let alone the neighbors kid, so it was basically a shock to the both of us. He immediately told her that she would not be allowed to even try that with our child, and to my knowledge, she said okay. I spoke to my husband in private after and he assured me that if he told her not to do it, then she won’t- but I am definitely keeping an eye out and being extra careful because it does cross a huge boundary for me. I would be furious if I caught her in the act, and it will absolutely ruin the stable relationship we’ve built with each other. I wouldn’t jump the gun and call her a pedophile or a predator, but I would say maybe she is just way too comfortable and also missing being a mom. Hopefully the boundary my husband and I have drawn with her will be respected.