As far as I know, Mormons have no dietary restrictions, and food is always welcome. I'm sure anything you bring will be fine.
Conversations: I would just express sympathy and be willing to listen to anyone who seems to want to talk. People often want to talk about their loved one who died, tell stories about her, etc. And of course, some people just want to be left alone. You have to play this by ear.
I would leave discussion of purchasing the house to your husband. If it comes up and he thinks it's appropriate to express interest, he can. You, as an outsider to the family/faith, would feel awkward (and probably be perceived as awkward) talking about this just now.
Don't say anything about the condition of the house. If people come over and are assaulted by the smell and lack of housekeeping, that's not your problem. Most likely your offer of hiring a cleaning company will cause offense in at least some of the relatives. Hubby might be able to get away with this; you probably won't. But whether the house is clean or not really doesn't matter and isn't your affair. Others will take care of this. You can trust them, and if they fail, it's not a big deal.
Can't help you on the Mormon funerals. You might be able to find something on the subject if you do a web search, though.
Best wishes and blessings to you.