What should I be expected to do to care for my MIL?

I agree with those who said you have a marriage problem. I also agree that you aren’t obligated to do anything here or meet anyone’s expectations. Do what you want to do. Help when you want to help, and do only what you are comfortable doing. And don’t let anyone make you feel guilty. My SIL married into a Portuguese family, really wonderful people but yes the culture is different from mine as well. They have certain expectations and a lot of responsibility falls on the women. The men are great providers, all hard working guys, really nice guys. But caregiving (of the children and elders) and domestic duties fall to the women. When my MIL entered hospice and there came a time at the end where her children were going to have to take over full care because her partner refused to give her the morphine, we all agreed we would take turns staying over there. No one was told they were expected to do this, we all just agreed that we would do it. If anyone wasn’t willing to do it, we would have been ok with that, with no hard feelings towards them. We ended up not having to do that, I think MILs partner decided that giving her morphine & being in control of it was better than having one of us there all the time and in control. Anyway good luck to you!

Any body can have any expectations they want. You are NOT obligated to meet other people's expectations.

Your MIL has 4 children who have decided to rotate her personal care. Good for them! That means in every 3 week period (21 days) your husband's turn will come up 5 times. In that same period he will have 6 non-work days. Works out fine, doesn't it? Sisters will have to take their time off on weekends, but that will suit them fine, I'll bet. And, if you feel generous (and NOT because other people expect it) you might spend one of those 5 caregiving days helping your husband with MIL. Since this is No Big Deal to your husband, he shouldn't have any problems with taking this on.

It sounds like you married into a family from a different culture. But you live in Iowa. Unless you specifically agreed to the expectations of your husband's culture when you married, it is reasonable for you to follow mainstream practices of the US. And in the US, forced labor is not acceptable outside the prison system.

As BarbBrooklyn observed, you have a marriage problem, not a caregiving problem. If you and hubby cannot come to terms by talking this out I think you might consider relationship counseling.

So... basically your husband volunteered you for a one-in-four hands-on personal caregiving rota, right?

You may not be in the mood for this, but I'm afraid my knee-jerk response is to laugh aloud.

You are not this lady's child. You do not speak her language. Are you a trained nurse or health care assistant? In what way, pray, are you remotely qualified for her, let alone you, to be comfortable in a close personal caregiving relationship?

Would you be happier, say, if you agreed to supervise your MIL's day with support from hired caregivers paid for by your husband? I'd say that's still plenty, and you'd be within your rights to say "not on your nelly" and make yourself scarce instead. But for heaven's sake don't think you are obliged to take on your husband's shifts - he agreed to them, not you. And never mind obligatory, I'm not even sure it's appropriate.

PS - it's not one-in-four, it's one-in-three, isn't it? I assume the BIL who attended the meeting is attached to one of the two sisters. How many shifts is BIL doing, do tell? And how come he was there and you weren't?

So if I am reading this correctly. Your husband and his three siblings had a meeting to divide up your mil's care between the 4 of them. Now your husband expects you to do his share for him?

Nope, not your responsibility at all. If he has to work on 'his' days, then he needs to take the day off work or hire someone to take care of her on those days. He entered into an agreement with his siblings not you.

Now you maybe facing an uphill battle, but you need to stand firm. On 'his' days, make plans for yourself so that you cannot possibly be available to care give.

It feels to me that you have a marriage problem, not a caregiver issue.

Your husband seems to think that the person he married would be okay changing his mom's diapers. Was this discussed before the wedding? Is this the cultural norm in his community?

You are allowed to say " no, I can't possibly do that". It's not about what's right or wrong, it's about what you can and cannot do.

I could never, ever, ever change an adult's diaper. Not my parents, not my husband. It's a deal breaker for me. No one is going to guilt or manipulate me into it.

Figure out what you can and cannot do.

Do you work outside the home? Have young children at hime?