Despite the pain both Kevin and Ian experience from their families, they are surrounded by the love given to them by The Major, John, Manny and all their friends from The Boot. These people are their real family that rescued Ian and Kevin. Knowing that Manny wanted to help Joseph to a better life, they want to give Joseph what others gave to them. For all the reasons you mentioned, it will be a challenging task for them to raise a preteen, but they have the strength, love and support to help them succeed.