Hate to break it to you, but you've got a long ways to go.
This fight is actually insanely easy. When fighting both Wesker and Jill make sure you have the grenade launcher you picked up in the ruins and a one case of acid rounds. For the first part, run around like bumbling idiot. If Wesker gets too close, shoot at him with the handgun and get away. The main purpose of the running though is to make sure Jill doesn't nail you with the machine gun (especially if Wesker is near you. I started off on veteran mode and all he does is a kick/palm combo which usually puts you in "dying" state and if it does- before Sheva can reach you -magnum...) So gather the green herbs, they'll come in handy if you screw up later, there's red herbs upstairs.
Get knocked through the door and run to your left. On your way, call Sheva. Keep going straight and she'll seperate from you and say
"I'll take care of Jill. You handle Wesker." This is actually quite simple. Wesker is strong, but as dumb as a sack of rocks when it comes to looking for people. Hide in the corners facing the doorways, making sure you're out of sight and he hasn't seen you. If you're close, wait till you see the first speck of black cross the threshold and fire. He won't dodge, he didn't see it coming. If you're too far to get a safe look without him noticing you, use your map. It is actually extremely useful and a lifesaver in this fight.
Sheva will hold true to her word and keep Jill occupied, but she does get back up eventually. So don't count on Sheva to help you with Wesker the whole time.
Careful when Wesker rushes at you though, there will be a reaction command to counterattack, but it happens extremely fast, there's no room or time for error, and you must be precise, I've only managed it four times myself. In other words it's fu**ing hard to avoid, so if you don't mind risking it and dying (Because this is the combo move I metioned earlier) simply run around him as he dashes toward you.
Now the Jill fight is completely blown out of proprtion. YOU CAN DO THIS FIGHT WITHOUT FIRING A SINGLE BULLET! -And I daresay it's easier. Just stay in the main area. She'll run around alot, but run around her and trigger the reaction commands and talk to her, eventually she'll resist the mind-control device and you or Sheva can restrain her. If Sheva does you can tear it off while Sheva's holding her which will give you an X-Box achievement (Miscellaneous fact if you're interested) or you can let Sheva flip her over if you wait long enough and tear it off while she's on the ground or you can restrain her and flip her over and tear it off while she's down. All methods work. Now be careful, if you don't restrain her well enough she'll kick you and it will hurt so make sure you have your reflexes ready to dodge when the reaction command appears if the situation arises. Odds are though, you won't be able to tear it off in one go, so when she gets back up, repeat the process and repeat until the thing comes off.
Lemme know if you have boss trouble in the future, these are my favorite fights.