Your options are essentially to deal with it or ask them what’s up.
Personally I wouldn’t waste time with co-workers who are being rude.
They could be jealous of your position for some reason or taken offense to something random you did. They may just be assholes.
At the end of the day you’re there to work and if it doesn’t affect that I wouldn’t bother.
If they are increasingly hostile maybe have a quiet word with HR.
Talk to a lawyer. But transferring the house to you with an agreement she can stay there till she dies is quite common here. And sidesteps all the inheritance stuff. But you often have to do it x years before she passes.
This is likely to get ugly and I would advise talking to your brother about it once you know what you’re doing so it’s not a big shock after she goes.