I still haven't beaten Khepri, so I'm going to have to figure something out.
As for Serket, I beat her with dual R. Minerva. Important things you'll need are a delay and as many board changers as you can muster. A damage enhance makes the last floor easier too. I can usually beat Sphinx with just comboing, but if you have true damage, there is no problem. Floor two isn't a big deal, but you need to focus on killing the dark guy and then stall the red dude out. Can stall here, depending on heart skyfall, but if you brought Tsubaki, all the fire will eventually kill the dragon whether you want to or not. Floor three is another good place to stall, you can tank the rage hit if necessary, but try not to. Floor four hits hard, so it is better to kill ASAP. Floor five is also obnoxious, as it hits pretty hard, but it is a dragon, so not too bad.
Floor six is where the fun begins. First off, you will generally resist the bomb orbs. Just work it down to half but try to keep your hp up. Once you are there, you can usually survive a couple of hits, so tank one or two hits (depending on your delay) and then delay and continue working it down. If it is water type, you can start hitting pretty hard due to 1/2 damage, I have beat it without a delay on water. If it is wood, you are screwed without the delay being up.
For Serket, I just stall for five turns. if you have hearts, eat some poison, use board changes with hearts to clear poison as necessary. Save your best board change (and enhance if you have it) until she is out of shield and absorb. 8 mil is a tall order for Minerva without a godkiller, but you can get there. Under most circumstances, either use the enhance then board change, or plan for a second board change. You should be able to tank her rage hit, but you will need something to get rid of the poison to mount a second attack.
For reference, my team: R. Minerva (Ilm)/DK Tsubak (Saria)/DK Tsubaki (Exa Hydra)/Gadius (Saria)/Anima/R. Minerva (Leilan). I think it is easier with the +RCV badge, but be careful of the big hits. Anima is there due to the damage enhance and godkiller.
