Mother of the Groom - Guest list!

You are not being unreasonable at all. This wedding is about you and your partner and it should be a day that matches your vision. If you don't have a close relationship with someone and can't picture them at your wedding then you don't have to invite them. No one is guaranteed a wedding invitation, and I don't think this sister is entitled to an invite if the only reason is to look after Nan.

Could your partner talk to his Mum, as it's his side of the family? Explain that you just want your closest family and friends at your wedding so unfortunately his aunt doesn't make the list. If he is clear that's the final decision and not up for negotiation then hopefully she will let it drop. If his Nan really does need support on the day then his Mum will have to make alternative arrangements. As you say, there may be other family already attending that could help.

If the groom's nan is so incapacitated that she needs three family members to act as carers at her wedding, then is she really up to attending a full wedding? Surely in that case, it's going to be enough for her to attend the ceremony, have a couple of photos and a celebratory drink and then go home. And if she doesn't need that level of care, then MILs argument is irrelevant.

I'm sure out of 55 people, there are going to be plenty of folk who are kind enough to give her an arm if she wants to move around. And even if MIL was the only person available, does Nan really need the loo so often that being the only person helping her get to it is going to be a full time job?!!! Sorry, it sounds to me as if this is just an excuse for MIL demanding the guest list she wants.

You could say they can come, if you have capacity, but ask the MIL to pay for them as you dont have the budget, or offer if you get any declines to then consider inviting them later. That being said, this is only to appease the MIL so if you do not want them there then I wouldn't offer, also, once you give in on one thing the demands will keep coming!

As others have said, there will be plenty of people who will help if needed. It is your day and your guest list, you are not being unreasonable and whilst she can ask, she should respect your choices and decisions. I think this is one your FH needs to tackle and speak to his mum, is not for for you to manage when it is on his side and there is clearly a concern over this persons attendance potentially causing a situation.