A couple of ideas I had are teddy bears, raggedy ann and andy, Winnie the Pooh, or jungle animals. I don't have twins, but my DS and DD do share a room. Their room is painted a peachy yellow color with white trim. The hardwood floor has those multicolored mats that puzzle together to cover it. DS is into trains so he has a primary colors Pottery Barn Kids quilt on his bed and his name done in primary colors. DD has her name in wooden letters above her bed in pastels and has a pastel quilt (pinks, light blues, yellows). I find for them it works well together and leaves us one extra room for the grandparents that come to visit a lot. Good luck!