That's great news for your sister's bird! I am sure she did the best she could for him, but you will understand his needs better. Birdie paradise

The lovebird might be more of a challenge than the budgies because of his history, so stay relaxed, don't expect miracles, and go at his pace. If you can get his wings clipped, preferably by someone who doesn't live at your house, that will make it easier and less stressful to get him back in the cage after he starts coming out. The reason for having someone else do the clipping is that the bird will be mad at that person not at you lol.