Grazzt
Demon Lord
Yes, but Miranda was signed on just before the buyout. Kim Mohan goes back to before AD&D, if memory serves.
Though I don't believe either of them has been there continuously since their first hirings--I know Mohan left for a while from the mid-80s to early 90s, and I think Miranda's been freelance for a while as well.
Steve Winter too (if it's the same one, and I'm guessing it is). He was there since the early 80s.