Where can I go to find money and sell of some or all of this trust?

The sale with a seller carry back note essentially triggers the taxable gain, but defers some or all of the taxable gain over the term of the note.  

We can sublet part or all of the space if we get in too deep as a "worst case scenario".

That being said, if you have increased expenses, it's completely justified to pass some or all of that onto your tenants.

Possibly you get the house you want in a seller's market, you get it for less, you get it faster, you get it easier, you get to work with a better realtor (or all of the above).

We have not got an offer on paper and an oral offer at 620K.

There won't be many, but occasionally you can find a deal....then you go look at it and see how much work it needs and see if purchase price,plus the repairs make sense for you to fix and flip.You can also set up your own searches for distressed sellers....you buy lists like the foreclosure list, or pre-foreclosure list, or post-bankruptcy list or all kinds of other distressed sellers...they you mail and call them asking if they want to sell at your price.You can also drive for dollars and target the ugly and distressed looking houses...and door knock, call, text and mail to them. 

Whether he is putting up 20% or all the money is immaterial, he is on the hook for all of it.Any equity at all is a good deal for you, maybe to buy in over time—which would help your dad.

Is $5K all you have... or all you have to invest? 

You can negotiate with the wholesaler to get some or all of it back.