Each machine will either have the same control or a version of the control type. If you can get all three controls makes and models that would help a lot since the post processor is based on the control.
I would suggest that if you do not have any post processor experience I would recommend you outsource this post to Intercim (G-Post) or another credible post processing business. A five axis post processor is not an easy task to undertake. I have been working with Pro/NC for many years and it is always a challenge to get the right information to the post (first things first), then get the post to output the right code to the machine. If you would like to talk more about this, e-mail me and I will get back with you. Good Luck!