Family whether blended or not is always such a touchy subject. We don't always agree and at times, we really don't know each other all that well.
The other option you might have is to tell them you will be happy to find them accomodations elsewhere, close to where your mom lives (at their cost of course). That way they can visit for short periods of time rather than barge right in on a woman who can't even care for herself, never mind entertain these folks for more than a little while.
Good luck dear....sounds like your brother will be able to handle things if they get to the point of needing to be handled HIS way
Hugssssss
J