Seller Finance Denied - immediate financing possible?

We're trying to help our Son and Daughter-in-law land their first home.  Seller financing hasn't worked, but seller came off price to $100k (was $125k). 930 sq ft 2br 1ba raised foundation on 1/2 acre - lake Livingston on one end of the street and Trinity River on the other end of the street.

How do we move forward to cover $100k mortgage?  Regular channels for mortgage will not work.... We were planning $600/mo mortgage payment, $100/mo insurance & $100/mo taxes - balloon payment in 5 yrs.

We are providing $5k to pay back taxes ($4k), back hoa ($125), pump septic & grease trap clean out ($225), survey ($600)  & our children are paying closing costs ($1500).

Deal stalled as owner backed out on seller finance.

Suggestions?