It's a terrible idea to leave a house jointly to siblings. I've read hundreds of posts on these legal sites where that ends up with sibling hostility and expensive litigation. But if it has to be done, it has to be done.
The problems with putting that kind of limitation in a will:
1 - It is difficult to enforce without the heirs spending lots of money on litigation.
2 - Probate laws may require an estate to be closed in less time.
3 - You'll need to pay rent to your siblings.
4 - Insurance companies might not want to continue the insurance for too long after death.
5 - The inevitable hostility between the siblings who don't live in the house and the one that does.
Your mother would be wise to consult an attorney to see how much of that can be overcome.
At any rate, even if your siblings decide on day one to sell the house it is likely to take some time to market it and a month for escrow, giving you plenty of time to make other arrangements.
Or, you can buy out your siblings' interest, assuming you have the money or can qualify for a loan.

