Sibling won't allow parent to visit any of the other children. Any advice?

You might want to talk to a lawyer specialized in senior abuse and neglect.

I'm an only child so forgive me if I don't understand how the 5 of you can't override one sibling.
He is clearly holding her hostage and, if the hospital has filed neglect charges, and she has complained about being hungry, you really have a problem. (I'd have beat his door down, but the that's just me.)

Get the law involved immediately. All 5 of you take the sheriff or police and go to the home of your brother. One of you need to be able to move mom in with you when she is removed from his home.
Contact an elder lawyer also. What your brother is doing is against the law. He could be charged with kidnapping.

I just don't get WHY you've let this go on so long.

1st thing call Adult protective services ASAP. 2nd What is the reason brother is giving for not allowing visits. (not that the reason is an exceptable one) 3rd Has mom said anything about feeling unsafe where she lives if she does call the police and be ready to have her moved to one of the siblings homes for at least until arrangements can be made to get her in assisted living/nursing home or whatever. As for the change in wills etc I presume that she is still mentally competent. Ask her if she is the one that doesn't want the rest of the siblings from visiting her and why. Is there been problems in the family before mom needed care? A lawyer will be needed for change of wills etc As long as mom is mentally competent it is her call where she wants to live, who she wishes to see or not see, eat carry out her life. Have you asked her why she is allowing brother to keep the rest of you away from visiting? What about all or most of you to ask brother if you can take care of her for a day or two in his home or yours. That way you get a better idea, exactly where the problems exist and why?