I'm going to ask my siblings if they got sick/have green poop from their parents party on monday
What makes you want to know about their poop?
I just want to know everything I can about people.
It's great to be curious about others, but some questions aren't appropriate and this falls into that category. Just because you're close to people doesn't give you free reign to ask whatever you want.
It's so funny how you are making such a big deal about it.
If this is the type of conversation that you share with them, then by all means, go for it. Generally speaking though, it's something that would make many uncomfortable. Just think before you ask, as you don't want to create an unnecessarily awkward conversation.