Two of my sellers want off the loan so they can buy again

Before you price a refi, send them back to their loan officer with the lease and twelve months of proof that the payment is being made from rents. Underwriting can sometimes offset a mortgage payment with documented rental income rather than counting it straight against them, and the answer depends on the loan program and the individual underwriter. Whether the offset works usually turns on who's receiving the rent and whether that shows up on their side of the paperwork, which in your structure it doesn't, so ask the question specifically rather than in the abstract. Costs you nothing and it's a real possibility that the block isn't the payment itself, it's how it was presented.

Worth reading your own addendum again. Mine says I'll use commercially reasonable efforts to refinance within 36 months and nothing more, and that language is the difference between a favor and an obligation. Also, releasing a seller from a conventional loan mostly isn't available as a product. Assumptions with release of liability are a normal feature on VA, FHA and USDA loans, and most conventional notes aren't assumable at all, so "just have him assume it" isn't on the table for the 3.375%. That leaves refi or payoff.

Price the option instead of arguing about it. You're saying the release costs you about 480 a month, so 5,760 a year, plus maybe 6k in refi costs on a 311k balance. If the seller's actual problem is timing rather than principle, paying him something to wait a year is cheap next to that.

The bind @orchard is pointing at is real though. The rent lands with you, so he has a mortgage on his credit and no offsetting income on his return or his lease. From an underwriter's chair he looks like a guy carrying a 1,640 payment on a house he doesn't live in and doesn't collect on. Documenting it doesn't fix that, it just explains it.

What I'd actually watch is which seller is more likely to escalate. A seller who can't buy a house and feels stuck starts reading his own note, and the paragraph he finds is the due-on-sale clause. Refinance the one with the lower rate gap and the louder voice, hold the tighter one, and don't let both conversations run at the same speed.

The one I'd think hardest about is the two sellers who haven't called yet.