I do not know, maybe the other ones were not holy angels or angels of God. I mean, they may have been evil angels that are doing the slaughtering. I do not know. It just seems that way. I thought it was kind of odd that just one of them they mentioned with linen clothing.
If you go back to chapter 8, you will see that He was showing Ezekiel, He took him in a vision, and He took him to Jerusalem, and He was showing him all the sins and the wickedness that was going on in the city. So that is what He was talking about here, and the ones that were marked were the ones that were mourning all the sinful acts, all the evil that was going on in the city.
Now this mourning is not just for the suffering or pain or sadness of life before the sinfulness that actually causes it. So the blessing is not upon all who mourn, but those who mourn actually regarding sin.