Family with a criminal record

My husband and I would like to set a long term goal of wanting to adopt (2-3 years down the road), so that we can allow our current children to get a little older and work on finances for the adoption. Neither of us has a criminal record at all, but I have a sister and brother-in-law that do. We currently don't have contact with them, but the rest of the family has been wanting to possibly open up contact with them. I'm nervous, because they have been unpredictable in the past. They have children, and I would like to be able to get to know them, but I just don't trust my sister yet. They say they've changed, but they've said that in the past as well. When it comes to the process of adopting, would it be better to just stay cut off from family like that? I don't want to have an "incident" come up because of them and then ruin any chances we might have of adopting. I don't know much about home inspections or how much they delve into family history, etc. Does your family reflect at all on you when they do inspections and all that? Do they look into it at all? We've been wanting to adopt for awhile and I know the basics, but no inner details or workings of what it's like to start the actual process of adopting. I just don't want my sister's screw ups to reflect poorly on us. Thanks for any help or advice!