You should try to seek a continuance of the hearing as soon as possible. It would also be wise to secure an attorney as soon as possible. Its sounds like the assignments here were similar to the robo-signing and fradulent document creation that has plagued the mortgage industry. The "VP for the day" execution by a party that is not employed by the bank is proof in that direction. I would also check the notary dates and compare it to the notary's expiration date. The original note would not...
You will have to request that the Final Judgment of Dissolution be modified to award support beyond your son's 18th birthday. However, once he hits 18 he becomes an adult under law, which does not favor additional support.
Unless the Plaintiff sought leave to amend the pleadings by joining the new lender and dropping the old one, the court only has record of one party. Clients are free to change attorneys and it seems like the lender wanted a new attorney, Also, play close attention to what you got in the mail. It might have been that the servicing rights changed, not the actual ownership rights. Or of the Plaintiff is a servicer, they could also service the new lender.
You need to consult with an attorney given that slight changes in the facts will change the advise. Even with an "as is" contract, a seller is legally required to disclose all known defects. This is what is known as the rule in Johnson v. Davis. An "as is" contract does not allow a seller to withhold knowledge of known defects.
This is the best time in history to be a defaulting home owner. Given that mortgage companies have a large inventoryo of foreclosed properties, they do not want more. You can negotiate many favorable outcomes. But all of the options would require an attorney to assist you. You can reinstate your loan with the lender or redeem the mortgage. Do not deal with the lender yourself.
Hire an experienced foreclosure attorney to take over your case. You are no more qualified to perform surgery on yourself than you are to take a deposition. Its your home that you are dealing with and there are no circumstances where I would advise you to take the deposition of a bank representative.