I'm assuming utilities are in your name as well since splitting up that would be strange.

So if insurance guy calculate to build the house is costing me $300 PPSF.Then in that case I have to buy house that costs me around $300 PPSF.In other word, if cash-flow property got fire, then it doesn't make sense to rebuild that house in 2023, because we only have the land value then, there's no point to rebuild if the FMV still less than rebuild cost....It feels so strange.

This all seems very strange - did you ask the GP why they are offering to buy you out? 

The house is quite old, needs all systems to be upgraded, and has an strange shotgun 2 bedroom setup.

It's kind of strange for it to have gone 8 years without making it to Tax sale. 

But it's not strange that the seller directly contacted the buyer agent?

And, saying that you do not by into turnover costs is really strange...

I've been acting like I'm the seller when the bank occasionally calls and it feels wrong - it's just getting strange at this point.  

Those last items are strange sounding to me.

It would seem strange to not be able to rent them out separately as that seems like the whole point.