My queries :
-If he can't repay loan, will our properties be seized?
This being a personal loan, the same would have been sanctioned in his personal capacity and not on the basis of the property, because the bank will obtain legal opinion from the bank panel lawyer before sanctioning loan on the collateral security of the property document produced before them. That time the fact that the property devolving on all the legal heirs of the deceased would be revealed and the bankers would ask the other shareholders to sign the papers on behalf of the borrower as guarantors. Since you or others have not signed any paper as a guarantor for the loan, the property cannot be seized by the bank fgor the purpose of recovery of loan..
-Are we legally responsible for repayment of his loan?
Since you have not stood as a guarantor, you cannot be responsible for his loan.
-Is there any legal way to separate ourselves from his financial decisions?
Remaining silent without responding to any call by the bank (in case they might try to implicate) itself would you keep you away from the liability.
I am worried that this can happen again and again.
Do not be worried, dont entertain his request anymore.