What territory does Tenpenny control?
We'll need to work on that. Me and Drop_Dead mostly.
Did he blow up Megaton btw.?
Nope, definitely not. The population of Megaton would have been absorbed by the Enclave.
Is the Captial Wasteland practically split between Tenpenny and the Enclave
Not really, The Enclave I would say should control the vast majority of it. However, Tenpenny Tower and some areas in the southern CW are in Tenpenny's control. Likewise, Tenpenny would have expanded south into areas not in the capital wasteland as well, although what those areas are would have to be determined.
With the Lyons BoS being wiped out or just a small faction nobody worries about?
They were nearly wiped out by the Enclave, but the remnants of Lyon's group and the full strength of the Outcasts fled back west to rejoin the Western Brotherhood of Steel. There is no Brotherhood presence on the East Coast anymore in other words.
NCR and Legion where pushed out?
Yes, both were pushed out.
Also, what's the premise of the convention? Why do we all of a sudden feel the need to meet?
Up for suggestions on that. I haven't really fleshed out the full details of the Convention's setting.