The facts posted suggest that the property belongs to your mother and hence, at present, neither you or your siblings have any rights in the property; she has the absolute rights and can deal with the property at her discretion.
Yes, you and your siblings are the legal heirs and could whatever property is left intestate after her lifetime. And no special rights or share has accrued and vested upon you just because you have taken care of her.
Of course, she can gift or execute a Will in your favour of the whole property or part of it; it is a matter purely at her discretion. But she can do those acts in respect of your siblings any third party as well.
More than the legal aspects, the situation posted warrants that all of you can join together and the mother can execute a sttlement deed to take effect after her lifetime and providing sufficient conditions to take her of her.