(ii)ExceptionsThe term “period of nonqualified use” does not include—(I)any portion of the 5-year period described in subsection (a) which is after the last date that such property is used as the principal residence of the taxpayer or the taxpayer’s spouse,

You want to find what references describe what the casita is (I assume an accessory to the primary SFR use) and then find other accessory to a primary use such as a detached garage or pool etc.

@Logan Parrette Unfortunately what you are describing has infected many markets and 'investors' are buying stuff that may never cash flow or provide much of a return.In our area everything within a half day's drive of Seattle is on fire.

If your property is described as a 4br with the assessor I wouldn't advertise it as a five.

Glad I never saw it - needless to say there is more to it than what that article is describing.  

MC are vehicles so he might not have considered them recreational vehicles (since you describe them as if they were street bikes they would be like having additional cars).  

From what you've described, it seems like your priority is to ensure they renew and the second priority is updating the rental amount for the below-market tenant.

I believe it is a great opportunity, as you have described.

The way you describe your arrangements reflect a business relationship and it is a good idea to treat those areas as such, separate from your romantic relationship. 

@Marc Middleton What you are describing is basically just wholesaling.