I used to think the same way, questioning why the hell they ever got together in the first place, when even their marriage on TNG was filled with fighting and doubts.
But my wife liked them, she liked Keiko for being a normal, everyday mother and wife who didn't give two craps about all the starfleet mumbo jumbo. I used to think they got into fights constantly and that's all their relationship was...... but after going through TNG and DS9 a couple of times, I grew to see that their relationship may not have been perfect, but it was "Real" in that they each had their concerns, their likes and their dislikes..... they had fights, but they were always willing to work them out and make their relationship work.
I can't say that my marriage has as many fights as they did on the show, but there were a few both my wife and I could relate to.... like the red dress situation, lol.... Guys don't care too much about what we do or what we wear, nor do we care what our wives wear or what they want to do.... so long as they're happy..... we're happy.
But the conflict occurs when the wife is tired of making the decisions and want us to pick something..... we don't care what we do really, so we after a while pick an idea out that sounds good to us..... then the wife either sighs or criticizes the idea and so we get more discouraged and don't bother suggesting anything in the first place, which puts the onus of deciding back on her, which creates the conflict in the first place.
Either that or we as the husband think of something we'd like, suggest it in a form of a question, and that in turn sounds to the wife that we're asking them to decide again, when we're just wanting to see if there's any opposition to the suggestion.... which of course ends up getting them more frustrated, while getting us frustrated at the same time.
Example:
"
Miles, I didn't say I was going to! I just meant I could use some."
"
That's okay. If you need to sleep, go ahead! I'll understand."
"
No, you won't. You'll be disappointed and you'll start brooding and stomping around like an Andorian bull."
He understood, he might be slightly disappointed, but he completely understood that she was tired and wasn't going to push it any further, but her being tired made her patience quite low, took it for more then what was meant..... it's a guy/girl thing :P
While there were moments that Keiko annoyed me with her complaining, but I saw over the episodes I re-watched that they both did care for one another and that both of them seemed the most relative to today's family and way of life them most others on the show.
As for Molly.... she seemed fine and certainly not a brat..... and if there was a time when an example was needed to show how united their family was, it was the episode "
Time's Orphan"