I can see 2 questions to be answered here:
- Who ends up controlling the Craterhoof Behemoth?
- Which creatures gain how much +X/+X?
First of all, whenever you have complex situations, it's important to remember how the Stack works. Any spell anyone casts, and every ability that is brought into effect somehow uses the stack. So whenever you and your opponent respond to each other with instant-speed spells or abilities, they are put on the stack, and only when neither of you want to play anything, the stack starts resolving in reverse order, i.e. the spell or ability that was put on the stack last will resolve first.
Let's say you control only the Deadeye Navigator and the Craterhoof Behemoth. Your opponent activates his vampire ability (VA), and in response you activate the Soulbound ability (SA) 3 times. That gives us the following stack, resolving from right to left:
VA-SA-SA-SA
SA is removed from the stack and resolves: Your Behemoth bounces and your creatures get +2/+2. You may or may not re-bind your creatures.
The next 2 SA fail to do anything, because the creature they were referring to no longer exists:
400.7. An object that moves from one zone to another becomes a new object with no memory of, or relation to, its previous existence.
Thus the 2nd and 3rd instance of SA have lost their reference and therefore do nothing. They are countered as they resolve.
VA fails for the same reason: Its target, the Behemoth, has changed zones, and even though it returned, it's still a different object. Therefore VA has lost all its targets and is countered.
Result 1:
- You control the Behemoth
- All your creatures have +2/+2
- The Behemoth has summoning sickness (new object), but for him that doesn't matter because of Haste.
Now I assume you imagined a different result: You wanted to bounce the Behemoth several times, so your creatures would get the +X/+X bonus several times. You can do that easily, but for 100% correct play, you would have to time it a bit differently:
When your opponent puts VA on the stack, you respond with only 1 instance of SA:
Stack: VA-SA
Then you both pass so the stack starts resolving:
SA is removed from the stack and resolves: Your behemoth is exiled and immediately returns. You bind your creatures again. All your creatures get +2/+2 until EOT. Your Navigator is 7/7 and your Behemoth is also 7/7.
Stack: VA
Both players have the opportunity to cast spells and abilities. You choose to activate SA again.
Stack: VA-SA
SA is removed from the stack and resolves: Your behemoth is exiled and immediately returns, but without his previous +2/+2, because it's a new object, as discussed before. All your creatures get +2/+2 until EOT. Navigator 9/9, Behemoth 7/7.
Stack: VA
Both players have the opportunity to cast spells and abilities. You choose to activate SA again.
Stack: VA-SA
SA is removed from the stack and resolves: Your behemoth is exiled and immediately returns, but without his previous +2/+2, because it's a new object. All your creatures get +2/+2 until EOT. Navigator 11/11, Behemoth 7/7.
Finally, VA is removed from the stack and resolves: It fails to do anything, for the same reason as before.
Result 2:
- Your Deadeye Navigator gets +6/+6, your Craterhoof Behemoth +2/+2.
- You control the Behemoth.
- The Behemoth has summoning sickness (new object), but for him that doesn't matter because of Haste.