Never have and never would trip with my parents...God- just thinking about it makes me feel uneasy.
However I have tripped with both my best friends father- my best friend was there (obviously), that was a bit fuck up actually. It was Christmas and I'm holding this 'orphans Christmas' for everyone who didn't have family or whatever to go to, so obviously there was a lot of drug use, eating etc. I was on heroin, ketamine and ethylphenidate as well as stoned as hell, having a good time then R, my best friend, turns up at about 4pm with his father. I notice in a second that they're fucked up and he tells me they story- they're at this bar and as they're leaving R finds ~350mg of MDMA in a baggie on the ground in the toilets. So him and his father, logically enough, decide to split it. Luckily enough it was MD and they were both rolling their balls off. It was pretty funny but also kinda weird, babysitting my gooned as best friends father while I'm smacked off my face.
I also tripped with my ex-gfs parents, both of them (they're divorced), separately. The one with the mother was weird as hell, she took acid with a friend of hers- they were punks in London in the '70s (lived across the street from Sid Vicious' heroin dealer- he once threw up green bile in their kitchen). As it happens I was over with my (then) gf for dinner- she had forgotten about this and when we arrived she was cackling away with her friend at the cat playing with its cat biscuits. When they started getting drunk we decided to cut our loses and eat a bunch of shrooms I had. Definitely the strangest trip I've ever had. Her Mum's friend was real cool, but really crazy.
We also took shrooms with her father- or more correctly, her father took shrooms with us at her birthday one year. That was cool- he was an old dutch hippie, he had heaps of cool stories about general weirdness back in the day. Like his flatmate going on an armed commando raid to abduct a friend of theirs back from a cult in the '70s, about a month after the place got raided and a small arsenal of weapons were seized or about living in Turkey and Afghanistan in the early-mid '70s. That was actually cool as fuck, a really cool group trip- about 15 people took shrooms and we all were on the same vibe, we sat around a big bonfire and had a BBQ talked shit and smoked tons of weed.