Thomas is so, so, so, so boring. There are SO many here. No idea how it is in the US, though. I'd probably like it if it weren't for the popularity- I find the sound of it quite attractive.
Mirella, on the other hand, I don't like. I just can't stand the Mir- sound, and I have to agree that it feels overly frilly. I normally love anything with
Ella in it, because I adore
Ella to bits, but not this one. I'd also find it too close to
Mira, personally.
Thomas goes well with
Joseph and
Leah. Your names are pretty all over the place, but I think that how sibsets go together is one of the least important things to consider. I love
Liora, it has such a great meaning.