Ending open ended AST and Regulated tenancy

Possession - Section 8 and Section 21

I am in the early stages of considering a purchase at auction. Unfortunately, the house is tenanted and being sold in that state with no guarantee of gaining untethered possession. I've looked through the legal pack provided and have several concerns. There are 3 tenancies, 2 are ASTs and one a Regulated tenancy. Even more worrying is that only one Tenancy agreement is provided with the pack, the others are missing and the one AST that is provided is incomplete in as much as the "Term" is left blank!! I will need to carry out fairly substantial renovations IF I go ahead. Has anyone any advice (other than DON'T!) ie Is it very difficult to end a Regulated tenancy and are there any obvious impediments to serving a S21 / S8 on the tenant to gain vacant possession? Any advice welcomed.