So i'm a little confused....

Chloe, Harriet, Kieran, Sarah, Danny & Sally/Amy are up for eviction

Four of those will be leaving....

But Jack thinks himself & the others are the ones who are really up and he has chosen to save "himself" effectively losing an immunity "card" for no reason? Am I following this right?

I think I am - I just want to be sure

Yeah, the HM's who weren't nominated are all up except for Jack who is aware of the twist and chose to use his immunity pass knowing he would have otherwise been up for eviction.

You're almost there. Jack was not originally up. He would have been in this group who are now up if he hadn't used one of his immunity passes to save himself. Jack knows about the twist and who is really up for eviction.

Not quite.

Because of the swap round, Jack would have been up with Chloe and Co - instead of Jade and Co who were nominated.

But BB told Jack about the swap and asked him if he wanted to use the pass on anyone affected, including himself. He chose himself.

They also told him not to tell the HMs what is going on.

Ok yeah i'm getting it now - so Jack would have been up with everyone who now is, but not one of them were nominated and 4 of the "non-nominated housemates" will leave while everyone who was nominated will stay with Jack - wow talk about a mess!

Complete mess