So I'm partly confused about the whole situation. I heard that if you marry someone they can make a shop which you gain money from. But then I heard you can use your marriage partner as a companion in battle. So I started to think, could you have a marriage partner (let's say Revyn Sadri) but then have Lydia as your follower? Can you have both? Because I need someone to help in battle, but I would also like to gain money from a shop. Any ideas?

Anyone you marry will open a shop you wont get to see the shop but you will be able to trade with your spouse, if the npc you marry is also a follow they will still be a follower as well as someone you can trade with.

Why do that? Have 3 females! 1 as your housecarl living in your house, Lydia for example, 2 as your wife, and the 3rd as your follower, Mjoll. That's what I did.

Haha! Cute. I'll have to give that a try.

Only followers you can marry can be your companions in dungeon delving and adventuring.

If your spouse is just an ordinary person, that's what they will be regardless of your marital status with them.

All married spouses will make a "shop" function wherein you can collect your share of whatever earnings.

I married Borgakh the Steel Heart. She was originally my companion, but then I made her my wife.

On top of that, I've found that the shop function stays the same, no matter what. Even better, the amount accumulates, so you don't even have to ask after it every day. You can come back a month later, and bam, a month's worth of earnings. And with Borgakh, I can adventure to my heart's content, and just ask her for whatever money the shop has made when I do need a little extra coin.

Three females, what is this "Big Love"