For Seath, if you have a good power bow and 500+ arrows. You can cheese him by circling around him and firing arrows. (If you are a medium armored character Btw).
Melee is complicated as I wait for him to do horizontal crystal breath and rush for his front and run back (repeat).
if you have a greatshield with huge poise, then blocking the crystals is suprisingly easy, all you really have to do is hold up shield wait for crystals, when they come go for belly, hit a few times, hold up your shield and back away. rinse and repeat!
I am so very frustrated with the bed of chaos or getting to her at the moment, I took the shortcut from the daughter of chaos and It takes me forever.. I solo'd it so far.. and I keep missing the jump!
Oh, for the middle part jump. Make sure the Bed of Chaos does it's attacks (as there is a delay between attacks) and run and jump a little bit right of the middle. You should land on the branch and not roll off and make sure to wait a bit, as if you run up it's nose will knock you off if it is doing an attack.
(Oh, the 2nd Bonfire (in the fake wall) you just run past everything. It is much easier than fighting a titanite Demon.)