Potty Training Dilemma

I have been half-heartedly trying to potty train Zak for a little while now. I really feel like he is so close to being ready for the whole process except for one big problem...he is OBSESSED with his diapers! He hates Pull-Ups and underwear. When ever I pull out underwear or a Pull-Up to put on him he cries, runs away, and brings me a diaper begging for me to put it on him. My initial thought was that Zak hates how it feels when he pees in the underwear which really is the goal. As soon as he does pee in underwear he will cry and take it off which should hopefully convince him to pee in the potty, right? But as I thought about it more I realized another issue Zak is having...he sees Ryder in diapers still and wants to be like him. When ever I get out underwear he tells me to put them on Ryder first.

The problem with this dilemma is that Ryder is no where near ready to potty train. We sit him on the potty periodically to let him try and go like Zak does, but he has yet to pee on the potty. There have been a few times where he will stand up, start to walk away and then pee as he goes. You can tell he has no control over it yet so there is no way we could potty train him. In order for Zak to go to any of the possible pre-schools or other classes he needs to be potty trained by his birthday which leads me to my dilemma...how to potty train Zak.

Last night Ben and I made the decision to go cold turkey with diapers for Zak. He seems way too attached to them and that is the first step to get him potty trained, I think. He will now only wear underwear (while at home and awake) or Pull-Ups (while out or asleep). This he had a meltdown when I put the Pull-Up on him, but I am sure he will get used to it.

Any ideas or suggestions?!