Perhaps a bit of openness and transparency? With all the other sblings?
I find that there is nothing like it when the thorny issue of money crops up. In theory, the other siblings should have no issue in allowing the money to be repaid from the estate- after all, it eased the fathers worries. In reality, my experience is that about 20% of beneficiaries turn into money crazed loons ( "its not for me , its for my children" is one of my favourites, followed closely by "its what he would have wanted" etc.,etc. oh, and anyway, didn't she get enough out of him when he was alive.........) the list is endless.
In the end, family politics will be the deciding factor. Mind you, its not helped by being described as a gift.
mf