Oakland Rent Control Tenant Illegal subletting Eviction?

[Evie Pylant]

Hi! I own a rent controlled Duplex In Oakland, and after a year I am finally in the process of moving into one of the units. During this moving prep process I’ve been by a lot and it appears my actual tenant must have relocated last summer without telling me and moved another group of people in. This group of people are loud, raucous, and have many other people over adding to the disturbance daily it seems.

According to the lease, (inherited from previous owner), my actual tenant was support be the only tenant, and is only allowed guests for 5 consecutive days. 

I realized something fishy was happening when one of the unknown people introduced herself as the house sitter, and mentioned the wall heater wasn’t working. I asked when was the last time she noticed it working...she said last September! So My tenant didn't contact me until February to say she had no heat? That makes no sense unless you’re doing something sketchy. 

What proof is needed to evict & does anyone have any lawyer recommendations for cases like this? Thanks in advance!