What are the buttons that I need to press in order to kill predators

You can build more convoys once you get access the the estate ledger.

At the accounting book , you can craft another caravan. Cheaply. First, go to your stock pile. You should see a list with categories on the right, and one of them will be labeled "forest." Buy 1 oak lumber and 1 oak bark, and then go to the crafting menu.

You will see something that says recipies. Press it, and it will lead you to another list. Go to the category that says "special items." From there, if you scroll right, you will eventually find an item that says land convoy. Then, just craft it.

You can have a maximum of three convoys at any time.

To be able to perform a double assassination, you have to be in High Profile. Low Profile kills will generally allow you to kill a single target. It's not automatic like it was in previous games. But it ultimately depends on the weapons used. But in the end, it all depends on if two enemies are highlighted and not just one.

With the (Double) Hidden Blade equipped, when two enemies are close to each other and you are in range of both of them, you must enter high profile and assassinate them. If you are on a higher elevation, it will almost always do a double aerial assassination.

If you are carrying a (loaded) rifle, you can kill two enemies if they are lined up one behind the other. It doesn't matter if you stay in high or low profile for this, you'll be firing a shot and that is always a high profile move.

I don't believe there are other weapons that can kill multiple enemies in a single attack.