She recently found out that she will be taxed heavily on the sale and is looking for ways to structure a deal so that she minimizes the tax impact.

TIC could mean that it is 1031 funds.Yes, any unique structures would be identified in the offering documents.One side deal could be some ownership in the GP but that does not impact you (unless they modified the splits to cover this additional investor compensation).Your diligence is good and the results are as expected...no deal breakers but a remaining level of uncertainty. 

.* You can have terrible neighbors who start a side business selling Meth or, potentially more impactful, have the next door teenager start their own garage band.* If your life circumstances change, e.g. your wages fall and you can’t afford the mortgage, then you’re stuck in the situation until you’re able to sell.* Have you ever seen those scummy “buy your home for cash” ads?

The last thing you want is a difference in opinions regarding how to handle a business related decision to impact your relationship with you partner, in this case your dad.

I learned the value of a impact driver.

No one can predict when the next recession will occur, nor how much it will impact housing prices.

If she finds out you are upselling it for a large sum, will the relationship be impacted?

Does the market you select not directly impact your ability to reach the goal?

I believe getting a HELOC will impact your credit score, so keep that in mind if you're thinking of getting a loan in the future. 

Could anything be passed down to family members without tax impact?