Will also have to buy a suite of appliances. 

I plan to convert an upstairs large closet into a bathroom, opening it up to the newly created master suite, making it a 2 1/2 bath home. 

-Full kitchen tear out and rebuild $10000-12000-All new flooring $3000-$4000-Paint $1000-A few fixtures $1500-2250-appliances $4000-roofing $6000-8000-Siding (is a maybe depending on how the rest of the neighbor looks) $3500-5000-deck repairs $1000- garage door $800-1500- Bothroom upgrades $3000Depending on the lay out we would be looking at doing master suite with a Bathroom.

Trees do have their own little slice of case law as they have caused many law suits. 2 rules to remember: if the tree hasn't fallen or you haven't contractually agreed to cut it there isn't a need for a suit.

Wondering if we could use a dormer (6-10') or 2 to give it more space and become a master suite or 2 beds.

This is not going to happen.....find a different, more realistic solution.Attorney time, maybe a Partiton suit, where if you guys can’t agree on a buy out between yourselves, the court sends it to a public auction.  

  - Seller can file adverse possession suit, get title, sale the property, and keep all of it

Would filing a quiet title work or could I file suit and if so who do I sue?

But you are just using estate planning and LLC's to work in the modern era to fight modern wealth destruction (law suits/judgments, healthcare expenses leading to long term care / incapacity, remarriage after death, death or remarriage of children.) 

Then I would recommend refining your investing criteria to what will suit your goals (flipping, SFH investing, multifamily, etc...).