Thanks so much, Michele for taking a look as well. I've agreed with the clients to not paint her braces. Hope I'll succeed there. I see your point on the importance of the sitters when one is painted larger than the other.
I know about the lighting issue. I'd have to add that slightly to the girl then as well.
I've come up with three more compositions, of which I quite like no. 7 (the clients left it up to me to put the dog in or not) and 8 (but what to do about that big empty wall space?)
Here they are:
http://www.sophieploeg.com/ALL.jpg(numbering is different there)
Thanks again. I find this really difficult, but am determined to bring this one to a succesful end. I really appreciate your comments.