I have a friend who I wouldn't say is at opposite ends, but she does do things very differently from me. I think she probably thinks I'm a regimented control freak mixed with sheer negligence, as I do bedtimes, mealtimes (roughly), naughty step, etc., but tend to let the kids go upstairs on their own, in the garden on their own, let them sort their own fights out unless it looks on A&E point, etc. Whereas she does allowing child to stay up as long as the tantrum will keep her there, inconsistency (imo), worrying about food non-consumption and being nervous about if they spill stuff.
I think the way we get round it is basically very rarely discuss parenting issues. We just talk about the stuff which interests us not to do with kids - mainly politics, feminism and our neighbours. And also, we don't comment on each other's way of doing stuff. When DS is there, I accept he'll do things her way, when her DD is here, she knows she'll do things my way.
The sex stuff is a bit of a specific difficult issue. I wouldn't mind if a friend told my DD/ DS about sex, but otoh I wouldn't consider it my business to tell their child about sex. Sometimes kids ask questions at an inconvenient time, though don't they, and I guess if you are trying to answer their questions honestly, it would be difficult to do without telling any other child in the room more than their parents would want them to know. I'd probably get round it by distracting, saying "we'll talk about it later, at bedtime - x hasn't come round here to talk about this, he's come to play - what about lightsabres?" or something.
However, with the sex stuff, some parents will tell their children more than your friend will want to tell hers, and they will then relay that to her at some stage, possibly earlier than your friend will want. I don't really think there's any way round that. But with the PG things, I'd just tell her that I don't want my child watching any non-U certificate stuff unless she's checked with me first. What you do with your own kids is one thing, but imo if you're going to show a ten year old a 15 film, you should ask their parents first, it's just common courtesy.