ivf twins with what quality?

Hi all I am currently 6weeks 6days pregnant with twins!!  We had our us last week at 6 weeks 3days and we were SHOCKED to find out we have twins growing in my uterus! We did reciprocal IVF (my wife's eggs my uterus) we received 10 eggs from my wife, 6 fertilized and by day 5 transfer we only had 2 embryos.  We got a good (4bb) embryo and a fair (3cc) embryo, the dr said if we didn't transfer both that the fair embryo was not good enough to freeze, so we decided to transfer both embryos.  Our dr told us that our chances for twins was very low based on quality of embryos, and hopefully implanting the fair embryo it would give implanting support to the better embryo.  We are thrilled to be pregnant with twins, but I'm so worried because I know one of them wasn't the greatest of quality and I don't want to loose either of them! Anyone out there have any success stories of lower quality embryos? Also who has twins and what we're your embabies qualities?