Just aged up my Sim's kids and they're also hybrids.
Packs I have are Island Living, City Living, Snowy Escape, Realm of Magic, Cool Kitchen Stuff, Luxury Party Stuff, the free Holiday Celebration and Ghoulish Guitar packs and Bust the Dust. I play on Xbox too.
I posted below the screenshots I took.
First screenshot shows her after I had her dive into the water to see if she actually was a hybrid (since both she and her twin did mermaid animations after aging up). Clicked her and as you can see in the screenshot she has both Magic and Mermaid powers.
Second screenshot is her standing on land after I had her swim to shore. She still has her tail.
Third screenshot is her moving (more like swimming) to a spot on land after I told her to go somewhere.
If it helps, my Sim had twins with Paka'a Uha and they're both Spellcasters upon aging up (and yes, my Sim is a Spellcaster).
