Alvor keeps trying to kill me, can't advance the story

If this is still happening to anyone, just run to Whiterun and pay the fine. Then fast-travel back to Riverwood and the problem will be fixed. Happened to my brother just there.

Usually, if friendly people are attacking you, it's because you've done something. you might want to check if you have a really high bounty or something.

You can yield to a (group of) person(s) by sheathing your weapon in front of them, and if your yield is accepted, they will stop attacking you.

I had something similar happen on the PS3. I accidentally stole a mug in Dragon's Reach and everyone started attacking me. I sheathed and unsheathed my sword but it didn't help. I fast-traveled to Whiterun and Alvor (along with the rest of the city) attacked me there as well. It seems like a bug.

My only recourse was to load from a prior saved game. I now tend to manually save regularly.

If you are on the PC, you can try this command in the console to bypass Alvor:

setstage MQ102 30

Other than that, you can try finding a calm scroll (or spell) and see if you can get them to stop attacking you long enough to talk to him.

I killed him. My story seems to be going along fine now. I just got past the Grey Beards and I'm currently on another quest. Seems to be alright. His family didn't seem to mind, either.