I guess they're not responsible for their mistakes. 

Call the salesperson back and make it his problem.

What is the value add to the builder for his time, management, experience, subs, etc.?  

If his appraisal comes back low, can I challenge the comps? 

@Chris Seveney thank you for your response.

While there aren't any real ways to remove the sister from the loan, here are a couple of tips you might consider:1.

So, I'm waiting and I'm asking what the status is and not getting any response from anyone.

But rest assured, any built-ins, any woodwork, doors and windows, anything "nice" in the house that you put it once upon a time for yourself to enjoy is going to get damaged.I am closely related to a guy who moved out of his house five years ago to a new house, with the intention to fix up the old property a bit and rent it, and yet his old house has sat empty for five years and he's paid holding costs for out of pocket.

I would ask him to review his documents from the seller finance to see if that financing is assumable.

Also, the terms of our offer were pretty ridiculous because it was contingent on:-Us finding two sets of renters and signing leases (in order to get the financing in order)-The owner of the offered-on property buying-out one set of his tenants-Us being able to move in within 60 days of closing How did you finance this deal?