Decrypting armour engrams with different classes
Solution 1:
Yes!
I did this not too long ago, just last week actually. I farmed 25 strikes on my 31 warlock for an exotic bounty. All armor engrams (and weapon engrams to level the cryptarch) went into the vault. Then I went onto my level 22 hunter (who needed legs and helmet) and decrypted all of them. Aside from the random Motes of Light and Strange Coins, it decrypted into hunter gear.