If you adopt a profile, you should update it as much as possible, add sources, bio etc. You don't have to work on the profiles for other family members for the adopted profile unless you want to.
If it turns out not to be connected to your family, you can orphan it again, you can keep it on your watchlist which means that you will get notifications of any changes.
You can work on orphaned profiles without adopting them.
Just be careful that you aren't creating duplicates.