Hi Linda: Great question... It's possible that two different Drs can have different recommendations, but since your husband has had a spinal injury, I would imagine that has a lot to do with the weight restriction. Once you've injured your spine most Drs limit your weight lifting amount; that also applies to people who have had back surgery, because your spine has been surgically manipulated and needs to be protected.
Ask both Drs what should be done, with regard to lifting heavy objects. I would think that neither your husband or brother should try to lift heavy things. If you have to lift something you are taught to do that by doing *hip hingeing* bending from the hips keeping your spine flat, or if you can squat with your knees that is safer as well also keeping your spine erect.
I would have your brother ask his Dr about this question and find out what he or she thinks about lifting, and how it should be done so that it doesn't cause an injury.
Good Luck