Because the loans are so new I would simply offer the actual cash /market value of the homes, and then assume the notes as part of closing (after having an attorney review their legal compliance). Had they been seasoned longer I would consider 50-70% of the full value.
Unless the Seller can demonstrate some reasonable underwriting, screening, etc there is likely a high risk these notes will not perform and then you have to foreclose and deal with the fallout…and that’s why you’re not going to pay market rates for those.