I recommend getting a structural engineer to look at it, not a general contractor.

The purpose was for us to fix up the property and to flip it.Ownership Structure: My aunt and I are joint tenants, each holding a 50/50 ownership stake in the property.

How would you suggest structuring a seller financed deal?

Even though it wasn't necessary because I always had a team that was doing the work that needed to be done physically.

Do they have a physical address? 

Any tips on structuring this with a secondary loan or financing approach?

For example FHA guidelines say you can deny an ESA if they cause an undue financial burden, cause a direct threat to the health and safety of others (the letter from the neighbor supports this), or cause substantial physical damage to the property.

Since this is our first property, is it advisable to use a single LLC for both personal asset protection and holding the property, or are there reasons to consider a more complex structure?"

Is it the overall tax structure or the growth potential? 

Quote from @Sean Regan:  I put this as a structural challenge in a scope of work.