NOT A SOLUTION - GENERAL STRATEGY
* Work together! I don't just mean that in the general sense, either! Throw your friends somewhere they couldn't get to alone, carry things for each other, distract enemies while someone else kills them, carry your friends around while they go use the toilet!
* Sacrifice your friends! Shrines to Kali aren't picky about their blood rites, toss your friend up on that shrine if you're short a damsel!
* If you die, don't give up! You can revive each other through the use of coffins located throughout the levels randomly, appearing starting only when a player is dead and in ghost-form.
* Ghosts aren't useless! By pressing X, or your whip button, a ghost can shoot out a puff of air, which is not as harmless as it might sound! Puff loot off of high ledges, stun enemies, stun your friends, push back ghosts, set of traps, or even knock an enemy into your coffin to set yourself free! They can even help light the way in darker levels!
PLEASE NOTE YOU DO NOT HAVE INFINITE LIVES.
At one point, your coffins will stop reviving your friends and instead spawn one of the helper-slaves you can purchase from the shopkeeper.
Personally I've made a lot of progress having second player dead the entire game, using the ghost to light the way, set off traps/enemies, push objects off ledges for me, etc. , saving revives for late in the Temple.
IF YOU'RE GOING IT SOLO, BE AWARE YOU CAN PICK UP YOUR FRIEND AND CARRY THEM WITH YOU!
Your normal set of 4 bombs and 4 rope is split between the characters playing, as well, so make sure to recover their equipment when/if you kill them!