Are legally bound to pay for a funeral out of a life insurance policy If the funeral was paid off by his siblings?

It depends on the precise details of the case. If the siblings paid for the funeral arrangements made by the deceased or the policy beneficiary with the understanding that they would be paid back, then the answer is probably yes.

If the siblings decided to hold an elaborate funeral without consulting you, and no representations were ever made regarding reimbursing them (including those formerly made by the deceased along the lines of "when I die, I want a 92-piece marching band to lead the funeral procession, I've got enough insurance to cover it"), then probably not.

Most likely this is going to require a civil case to sort out, and you should contact an attorney.