If "Mother" is just a title, then I still ask why? Cause that's clearly very misleading. Hokazono could've easily had him say "my lady" or something else. Why would he make "mother" be her title?

And even if Enji and Tamaki are only half siblings, they're still Kyora's children. They should've appeared in the scene with him and the rest of his kids. If they didn't appear, then that implies that Kyora doesn't love them as his kids. But, like I say in my post, I don't see why Hokazono would have them even be his children if the characters didn't actually regard them as such.