Are you able to speak to elijah at the end cause everytime he just goes hostile kinda annoying

You can have a pretty lengthy conversation with him when you're in the Vault, and he's a hologram. After that, no.

It seemed kind of hard NOT to kill him. I mean I found it kind of difficult to convince him to stand down and I think it was meant for us to kill that ghoulish bastard. It's not like he was a nice guy...

You had to respond in a "nice" manner in dialogue options.

Wiki says ■His ego is very fragile, and the player is encouraged to take care not to bruise it when dealing with Domino, lest it carry dire consequences down the line.