I think it is a cute sibset, but like
Kristen I prefer to spell
Katia as
Katya or
Katja. I also think that the mn's seem a bit like filler mn's, but they are cute and strong and seem to work well.
I have heard
Lucia pronounced Loosha but more often I have heard it pronounced Loo-chee-uh, which I believe is a legitimate pronunciation. I will look into it, but before you decide on a pronunciation you should look into it more. It would be horrible if you name a child something and someone corrects you on the pronunciation after the child already has the name!