The only time I've had aggro issues, was in Utgarde Keep with a level 80 druid tank, and a level 70 healer (and dps).
Was attempting to continue the boosting of a team.

Unfortunately, the mobs did not like the level 70 toon casting any form of heal and would drop aggro on the level 80 as soon as any heal (even just a Renew), even if they were half dead without any other toon in the group having touched them.

Was pretty frustrating, and proved to be the same in WotLK dungeons with the same group.
I ended up just running them through quests to level.

I've not had an issue with threat, with same level and comparatively geared toons in quite a while.
Blizzard doesn't like the old EQ mechanic, where the tank has to battle for threat and the DPS has to watch their threat constantly as a mechanic in every raid encounter.



With only your Bear in melee, things should be a lot easier for you.
Your DPS and Healer can stay at range, so you won't have to eat many cleaves or PBAoE's from the mobs.

I'd probably just refresh Earth Shield and put the HOT on the bear.
Have the shammies drop totems.
And charge in with the bear.
Include some swipes in your spam/rotation, and have the shammies either stick to their first target or just auto assist the bear on whatever it is killing.
Sticky targeting can be strong, when you want to burn one thing down (that the bear has enough threat on) while you pick up an add or whatever; straight assisting whatever the bear targets is easier to set up and works too.

You could have Tank sequence only, on Key 1.
Tank sequence and DPS sequence, on Key 2.
If you're using in-game castsequences for the tank, pressing either Key 1 or Key 2 will have both (identical) sequences advance at the same rate.
Once the tank has initial threat, switch to Key 2.
If you have threat issues move back to Key 1.

You can also consider having a key or keys, where the DPS assist your healer.
Having each of them Chain Heal a party member, can help with AoE.
Or possibly each assists the Healer, and casts a quick heal... or assists the tank, and then casts at the mob's target [@targettarget,help]
Not a bad option to include either/both, as a hotkey to have available.