I know that the loss is overwhelming right now but I think this is great that your sister is going to pass them back to you. I've lost several members of my family. I can understand your feelings that you are going through right now.
If I was going through what you are going through right now, I would not make any decisions at this time. I would put the quilts away in a closet and wait a year. Then I would make a decision. I think that you will find that you will have a different outlook about the quilts. You may, at that time, give them away but when you do, you won't have tht overwhelming feeling of loss. I think that seeing the quilts in a year will give you a warm feeling of love that you had made those quilts for your mother and how much she enjoyed them.