Is there a way in Islam to protect my father’s flat from being claimed by my siblings after his death?

Assalam-U-Alaikum. We are 2 brothers & 1 sister in my family.We have one flat which is on my fathers name, where I stay with my parents.My brother was in need to money to buy his own flat, for that we decided to help him. For that we fixed our fathers flat price as 30 lakhs, and considered as 10 lakhs each for 2 brothers & 1 sister. So i kept the fathers flat, and paid 10 lakhs each to sister and brother. Now brother has its own flat on his name. But this flat which i purchased from my father is still on my fathers name. My father says let it be on his name only, and he just signed on one blank paper that this flat belongs to my younger son (me). Whenever my father is not in this world, can my brother & sister can claim their share in my fathers flat, which i have owned but still on fathers name. Is there a solution for this, where in Islam, I can avoid my brother & sister claiming for fathers flat later. May Allah make my father live longer happily & on Islam. Please advise me.