if you played the game you'd remember comstock was "shooting blanks" because he passed through 1 time too many. so i kinda think they are the same, but i also hope not because i think they'd be a good couple. Plus if things go ok they are going to have some smart ass kids.
Since I'm currently taking a genetics course, it is kind of fun to think about what the child of two completely identical parents would be like. The theoretical child of the Luteces could probably be a genetic "clone" of either one of them, or possibly express some recessive traits that the parents didn't express. There's also the possibility that they, like Comstock, have become sterile due to prolonged exposure to the tears. Yeah I think I'm probably looking into this a bit too deep... Let's just call it selfcest and call it good! ^^
" When all else fails and no one understands you, at least you still have yourself." This is how I see their relationship, just two souls that couldn't find anyone to fit with, until they found each other.