When I visited the property, my (investor-experienced) agent gave me some rent estimates for the property's units, but they seemed really high to me and seem out of line from what I've seen the market absorb.

The special assessment seems high in general, so which building it is would help provide some insight into why and what you gain from it etc.

I’ll still come out with a good profit, but to sell a, sometimes, high cash flowing SFH with a 3.75% rate also seems crazy.TIA!

I'm not sure about that particular group, but I would highly recommend contacting one of the tax pro here on the Bigger Pockets forums. 

While I'm relatively new to REI, I bring with me a quarter century of lessons learned in running high-performing teams, managing projects, and getting things done. 

Seems fishy as email doesn’t match website (which is a .online) site and no pictures of principles (who have linked in accounts)

I also highly suggest teaming up with a broker who you'd want to build a relationship with and truly understands the ins and outs of different underwriting guidelines.

As to the original question where to get the data  I highly recommend Property Radar  check it out.

She does not have money for her expenses and is borrowing at a high rate of interest which is becoming impossible the idea is to sell my cousins rental property take a boot to cover her expenses and the rest ($750,000) do a 1031x.  

If you are carrying a high note and this is indeed your only investment I do not think there is an issue keeping this in your name.