Agree with Rookie, that I wouldn't do 'Join Up' with this horse, at least not if you don't have a VERY good understanding & feel for what's going on, and you don't have a definite goal, aside from gaining trust & asking the horse to come to you/follow you. I too think there are far better, easier ways to accomplish those things. If you do have that definite goal of what you want him to learn by chasing him around a round pen, I would work on gaining his trust first anyway.
He will even slow down for if we tell him easy. He gives all the signs that he wants to join up, head lowers, ear is toward us, mouthing, but as soon as we stop, he will stop and look at us but will not come close.
Slowing/stopping is an important part of lunging, not at all an 'even' IMO
& I'd say that if he doesn't know how to do that, you're not up to lunging.
The 'signs' you describe are just signs of submission/resignation, hopefully signs of understanding that you want him yielding, not trying to kill him
. 'Joining Up' is your game, your aim, not his. 'Drawing' him to you or otherwise motivating & reinforcing him from approaching you will teach him to come to you, if that's what you're after.
but I am not sure that we are doing it correctly. Although, our friend came out and showed us how to do it, it is easy to make a mistake
A very good reason not to bother IMO. I think it's important to have a very good understanding of the process, reading the horse & reasons for when to be, why to be... why not.... before trying this.
I'd personally be starting with a horse like this by just hanging out with him, doing 'stuff' around him, getting him trusting of being close, allowing to be touched/brushed, handled, etc, teaching him first that you're a Good Thing to be close to, that he's safe & it's Nice for him to have you do stuff with him, before I'd start asking him for Work.