I usually use a site for names that have not too common letters like Q and really, the one I use the most doesn't have more than. Since your son has such an odd name, I would stick to odd names so one of them doesn't question why you possibly "love the other child better." I've got a friend with a very odd name who feels so strongly that their parents adore their siblings more than they adore them.
A few other names I've found that aren't in the list above are
Really I wouldn't give them another Quin/Quen name as one may want to go by that as a nickname.