This sounds like a somewhat convoluted situated that got real messy.
If I understand this correctly, you sublet your apt to two people, with a friend handling the affairs for you. Doesnt sound like either you or him screened properly for sub-leasers - you have to act like a landlord and find people who are most likely to pay rent on time every month. You said that person A was always late - that's was an initial red flag right there. It also sounds like person B was the responsible one(?) and they left, leaving you with two non-paying subletters in A and C.
It's the landlord's responsibility to evict, but *you* have been paying him or her every month on time, and its still your apt. So why would he/she evict? I agree with Greg that you'll need a special lawyer thats well-versed in subletting to advise you. Verbal agreements are legally binding, but you'll need a paper trail (payments/receipts) for proof.
As far as the eviction goes, if I were you, I would talk to the landlord and let him know you will not renew the lease after July. Once July ends, the landlord will need to serve a Notice to Quit which gives all tenants 30 days to move.