My brother died last year, and I'm still nowhere near getting it sorted out. He was on his own, which made some things more complicated, but other simpler.

The main thing here is looking after your sister. You don't mention if there's any other family, but you seem to give the impression you're on your own in this. You need to have someone you can trust to share the practical stuff of the funeral and so forth if at all possible. I was very glad with my brother that since he died back in a rural community in Ireland there was a well-established pattern of dealing with all this, whiuch made it a lot easier.

For other business affairs, encourage your sister not to rush things, because as InOBU said, it's easy to make mistakes that way.