From The Tale of Years:
circa TA 1300
Evil things begin to multiply again.
Orcs increase in the
Misty Mountains & begin to attack the
Dwarves.
circa TA 2480 Orcs begin to make secret strongholds in the Misty Mountains so as to bar all passes into
Eriador.
Sauron begins to people
Moria with his
creatures.
TA 2509
Celebrian, journeying to
Lorien, is waylaid in the Redhorn Pass and receives a poisioned wound (from Orcs - Fellowship Of
the Ring, Many Meetings: 'Elladan & Ellrohir.... forgetting never their mother's torment in the dens of the orcs.').
TA 2740 Orcs renew their invasions of Eriador.
TA 2790
Thror slain by an
orc in Moria.
TA 2793 War of the Dwarves & orcs begins. Appendix A,
Durin's Folk: 'When all was ready, they (the Dwarves) assailed and sacked one by one all the strongholds of the Orcs that they could from Gundabad to Gladden.'
TA 2799 Battle of nauduhirion before the East-gate of Moria. Again, durin's Folk: 'He (
Azog the
Goblin) saw that all his host in the valley was in a rout, and the Dwarveswent this way and that slaying as they would, and those (
goblins) that could escape from them (the Dwarves) were flying South, shrieking as they ran.'
TA 2800-64 Orcs from the North trouble
Rohan. From Appendix A (The
Kings of
the Mark)
Brytta: In his time there was war with Orcs, that driven from the North (obviously, the Misty Mountaians) sought refuge in
the White Mountains.
The
Hobbit: (TA 2941) 'Both he (
Gandalf) &
Elrond had been well aware of the presence of evil goblins in that part of the mountains. But their main gate used to come out of a different pass, one more easy to
travel by, so that they often caught people benighted near their gates. Evidently people had given up going that way, and the goblins must have opened their new entrance at the top of the pass the Dwarves had taken, quite recently, because it had been found quite safe up to now.'
Ok, so we see that the Goblins were always there in a small remnent, probably those that originally fled or survived The War of Wrath at the end of the First Age. The Misty Mountains was a likely spot to come down from the North into, just as the Balrog had.
When Sauron arises, they began to multiply again......
Are they under direct orders from him?
It appears when Sauron returns from fleeing into the East at the end of the Watchful Peace (2480), he steps up his strategy in the Misty Mountains, including Moria, barring all passes, leading to capturing Elrond's wife.
After the War of the Dwarves & Orcs wipes out a good amount of the Goblins, they regrouped & reproduced until the Battle of Five Armies, repopulating their strongholds.
They again did this after the Battle until the War of the Ring & "only the Beornings keep open the passes" Gloin tells Frodo.
So, yes, we can say that blocking the passes was a general order from Sauron, but not specific to the Dwarves Company.
As far as the trolls, William says "You've et a villiage and a half since you came down from the mountains" and all they do is argue over food, so I would say food is the reason for their movements.......
Plus, let's remember trolls are dull-witted, so giving them a plan wouldn't be a great idea.
Thirdly, Sauron did not have many agents in Eriador & how would he even be aware of what Thorin & Company were doing?