Evicting Squatters

[Buu Quach]

I have a property I just got under contract and the seller has what she called a "squatter" in the house. Initially, the "squatter" was a tenant that had signed a lease with the seller. The lease has since expired and the tenant has not payed rent in over 4 years. The seller no longer wants to deal with it, hence why she's selling it. As I understand it, she recently just sent an eviction notice to them.

Does anyone have any experience with squatter laws/rights in Texas? 

1) What would be the proper approach for me to get rid of them and how long would it take?

2) Would there be any legal way for me to see the inside of the house before closing on it?

I've considered cash for keys, but not sure if that would be a feasible approach here.