To the best of my knowledge, there is no way to link your accounts together (e.g. a blanket account such as Battle.net accounts). If there was, I would have done so. I have two accounts, both in my name. Each has a separate e-mail address for logging in.

However, if you have a key-chain authenticator, you can link up to five accounts to the same authenticator. This is not the case with the Android app (which I also use).

Regarding your second question, think of it like this: If you could both do your class quests simultaneously and receive credit, it would be advantageous to exclusively group with other players who are your class for the purpose of completing class quests (unless you are only in it to the see the story). If you help, say, a smuggler complete his/her class quest and you're a Jedi Knight, it would take twice as long for the two of you to complete your class quests. I am assuming Bioware thinks that simply having a party member who is the same class doesn't entitle you to finish your quests any sooner than if you were grouping with a different class.

EDIT:

Also, I might have misunderstood you, OP. I thought you were asking if there was any way to receive credit for helping another person of your class complete a class quest that you have also. The above poster is correct in that you can physically enter the same instance if you check that option, although only one of you will receive credit, and you will have to repeat the instance twice if you both want credit.