I just finished reading the Petaybee books. It's kind of a double trillogy. I read the first 3 a long time ago, but just read the laterest 2. I know I said trillogy, but it's obviously going to have another book. Powers that Be, Power Lines, and Power Play are about the parents. Changlings and Maelstrom are about their twins. The dad, Sean, and the twins, Roran and Murel, are selkies, shapeshifting seals. Also thier home planet, Petaybee, is senat. They are very interesting books but Maelstrom ends in a chiff-hanger. So I'm waiting for the next one.