Why should a caregiver accompany family members to take Mother out to dinner?

Consider doing take out and having one person or maybe two at a time at her place. Changes in locations or if there are a lot of people in the restaurant might not work out so well because its different and that could make it hard on her. Maybe have more but individual visits, rather than just once every 5 weeks? 5 weeks can seem like a long time.

OMG a family member wants to take Mom out and give the current caregiver some respite!!! What am I missing? Let them give it a try and see how it goes.
To give another side of the tale, I used to get annoyed when my sister came from out of state to visit Mom. When she wanted me to come along, I felt that this was MY free time. I felt sis should have alone time with my Mom.

Maybe it is time to stop the every 5th week dinner out. Tell them that Mom is unable to leave the house as she is in her final stage of Alzheimer's. Use a therapeutic fib and tell the family that Mom was very difficult to control after she came back from the last dinner, and it is because of the Alzheimer's. And you don't want to put Mom through that, again.

Tell them they are more than welcome to bring dinner to the house. Olive Garden has carry-out menu, as does other restaurants. That would cause less confusion for Mom, or maybe not with having more people in the house. Maybe it is time when just one person at a time comes over and brings supper for Mom and you.

It would certainly help to have a caregiver/someone familiar to accompany your mother on these outings. They are a lovely idea, but if she will be only seeing them every 5 weeks, she might have forgotten who they are in between. No, you are not keeping your mother from seeing them, but are just going to be there as a familiar face. If they object, let your mother go and see what happens. The siblings may not even notice anything is amiss. They can deal with any unusual behaviour as well, that is putting the cat among the pigeons!!!