Hi I have a question regarding parabati.I was wondering are all parabati as close as Alec/Jace and Will/Jem? I know not everyone has one but is there ever circumstances where they aren't as dedicated as the pairs we've seen?

I think of Jem and Will as closer than Alec and Jace. Not that Alec and Jace are not close! — they very much are so. There is a lot of sincere love there on both sides. But that “you are the other half of my soul” business of Will and Jem’s is because they are who they are, not because they are parabatai. The parabatai bond just amplifies it. 

Keep in mind Luke and Valentine were also parabatai, and Valentine was willing to kill Luke. Then there have been parabatai who fell in love, and probably ones where they started to hate each other. Being parabatai doesn’t make you love each other. Ideally you become parabatai because you already do.