Second, it sounds like when you and DH visit your ILs, your husband and FIL "disappear," leaving you to deal with MIL.
It does appear like this. I can understand it from FIL, but you need to talk with your husband and be very factual about things so he doesn't wave it away as nothing major. Talking with MIL might not have much point if her memory is going. Ideally, decide on a phrase or something where he'll know you're at your limit so he can take over. "DH, MIL hasn't had much of a chance to talk with you yet" sounds harmless enough to anyone else.
My grandmother was like this. She would suddenly appear next to me and clutch my arm in an iron grip like we were best friends (despite always being rather aloof in the past), and would press her whole body against mine while stroking my hair and getting her hands irrevocably tangled. It was horrible, and not something I could endure for hours on end. I would just instantly take a few steps away while smiling apologetically. "Sorry, I just did my hair and I don't want the style to fall apart yet," "my arm is sore from the gym yesterday, please don't touch it," or similar excuses would sometimes be said to stop her simply walking back to me and repeating the behaviour. I've never styled my hair in my life, but it got the point across, or at least stopped her rubbing her hands over it.
Endure what you can, but don't feel like you have to put up with very major things, like following you into the bathroom and so on. Sure she's getting old and out of touch, but that doesn't isn't a free ticket to do anything she wants--use small things to prevent her going too far as soon as they occur. I found sitting down together was good, because I could distance the chairs somewhat, and she wouldn't be able to suddenly reach out and put her hand on my face. Shorter visits were good, too.
I hope you can find a way to work this out. Talk with your husband first and foremost, though, so you're both on the same page. He might want to dismiss it (it can be hard to accept), in which case, you might have to be unavailable for future visits until he decides he's able to support you.