Selling and buying something else you want keep and doing a cost seg in would help with the tax burden probably better in this situation.

In case I have to sell or I quit running STRs I wouldn't want to be under water out the gate.

I wouldnt want to sell unless I needed the funds for something else .But it doesnt hurt to ask them if they want to sell 

So in my mind it would be best used as a last move into a REIT you never sell.  

Additionally, your brother would inherit your cost basis in the property, which could result in significant capital gains tax if he sells the property later.

I understand it become tad difficult to refinance since some lenders wouldn't lend on the home in trust, but is it easy to sell a home in a trust, just like you are buying in a trust?

Selling one and buying several is fine. 

This means I can sell my share independently.

And it can work really well for you as long as you pay attention to the statute requirements.In order to defer all tax you are selling investment real estate and buying investment real estate of at least the same value you sold. 

I think it would be better just to stay on good terms and let him know you will contact him when you are ready to sell.