When it comes to family matters, Tai does seem to be having supportive parents (see #2258 Verstiphobia). I suppose it was her friends (or rather, bullies) at school (#2263 Every One Has A Story) and later, the polyamory scene at university that got her into the recreational drug use. hmm I just read those comics again, and they seem perfectly normal. Why am I trying to prove Tai has a problem?!
If it's a fight between Marten and Dora, one could argue that a lot of the sibling rivalry could have stemmed from Doras parents (then again, Sven does have it pretty easy). I'm afraid to say that, in the absence of any contrary evidence, it's Marten, because he does seem to have a pretty awesome family (especially considering Veronicas reception speech). My mom was a closeted lesbian as well, and, while the immediate time after the break up was pretty horrible, I love my parents above all and I'd never consider them bad parents because of their break-up.