Can I join BoS, Minuteman and Railroad at the same time. Will it effect the relationship between the factions? Like will they attack me if I join other factions, do their questline? I need a lot of details.

You can join them all up until a certain point. Ultimately they all want to kill each other (BoS want to wipe out the Railroad, Railroad and the Minutemen want to wipe out the BoS), so you'll have to choose a side eventually.

There's a fourth faction but idk if that's considered a spoiler, depends on how far into the game you are I guess

well, screw bos then. So I can join BoS and kill them later right? But I read that Piper hates you if you join them :/

BoS all the way. I love how in depth they are in this game, i have always been a fan of them. Now i can hang there banners in my house, and even adorn my armor with the logo.

BTW, this handle has been my xbox live name for like 8 years

So don't bring her along when you join.