Buying portfolio sitting tenants advice

Rent Arrears

HI, we are speaking to a landlord to purchase a large portfolio, the majority of the tenants we believe are council tenants and occasionally some dont pay which sets alarm bells going as he said some live hand to mouth, but as the rent per month is huge the landlord lets it go. An amazing position to be in.
But my question is, If the tenant is council and they dont pay there are processes to get the council to pay direct,
But if its a private tenants and the landlord doesn't have his paperwork together what is the process and timescale of getting them out if you dont have the proper paperwork? and avoid them trashing the house?
I suppose the very worst scenario is they are illegal immigrants ?
We have a long way to go on due diligence in terms of viewing, checks on everything incl tenants but this is a concern, we are also looking for equity partners