Do NOT trade Oswalt for Lopez and E. Santana!
Biggio is definitely a weak link, but it's not worth the trade. Biggio's OBP is comparable to Lopez's anyways, so in your league (and at a weak position), the upgrade isn't worth it.
You might consider trading Podsednik. Maybe you could package him with Washburn or Wakefield (not that they'll add much value) to upgrade a little bit.
I'd also start Shelton ahead of Granderson. Ride the rookies when they are playing well, but don't rely on them for the season.
You've got a nice top of a rotation, but the back-end is a bit weaker. Keep on top of the waiver wire for better SP.
MacDougal is injured. Put him on the DL and see if A. Burgos (MacDougal's replacement) or Miceli are available, if you need saves. You might also grab Devine if he's still available, as he's likely to take over the closer role in ATL at some point this season.
Please help me too
"The game has a cleanness. If you do a good job, the numbers say so. You don't have to ask anyone or play politics. You don't have to wait for the reviews." - Sandy Koufax