Is mf shared when partied or individualized. Also, is identifying with Cain any good?

If by "mf" you mean the "Better chance of getting magic items", then it's personal, only shared with your mercenary or pets (they use your mf for their kills, mercenary also adds his own).

In party, however, you have better chance of dropping items. Each monster is more eager to drop something than nothing.

When an item drops, its stats are stored. The manner you identify it has no importance.

thanks bro