The existing graphic shows through slightly on the turquoise onsie, but I don't think it's a huge deal. I'll have to take that into consideration when choosing my images for future projects of this sort, and make sure the images I choose are dark where they need to cover something.
Took some long sleeve shirts and cut the sleeves and made the girls some princess shirts.
These are the Iron on Transfers I use. I've done a lot of projects with them and they seem to hold up pretty well and not crack or peel off. I've found they are the cheapest at Wal*Mart.