Upside down looking for sale options

I have a SFH, a triplex, and two duplexes in Greenville, SC area that I’m still upside down on (owe more than they’re worth). Do I have options to ease my monthly cash drain? some thoughts:

  1. Owner carry sale to an investor vs Sub2
    a) If the sale price doesn’t cover what I owe, can it still be done without me coming up with my own cash to pay off the existing mortgage?
  2. Selling the note - I would certainly get less than what I owe here. do note buyers ever “carry back” a second private note for the balance?
    (Example: I owe $300K, note buyer pays $200K and I make longterm payments to the note holder for the other $100K, since he paid the existing mortgage off to get the note)
    Thanks for any help folks