re: Take former business partners idea or bring him in... again?

did you ever sell any of them (whatever it is) in the first iteration of the business? if you did, then your patent application is out the window without enough changes to the original concept to constitute a brand new patent

reach out to a patent attorney and ask for a consult

they can research prior art and tell you whether it is worth pursuing or not

if it is, the patent attorney will start the paperwork

then get an attorney and ask for guidance on the business aspects of this

and stop asking the OT for legal advice