All 4 of the monsters in the area repop, kill them all until all 4 are "a Steward of the Seal"
They WILL depop so once the "a Steward of the Seal" has spawned it will be replaced by a non-steward if not kept engaged while waiting for the others to spawn (not instantly but <5 min). It is a good idea to bring a mezzer to do this, but it can be done with 2 mages rooting all four stewards.
With all 4 of the stewards up get all of them down to about 20% life then kill them all quickly around the same time
Grash, Timant and Tival will spawn in a single encounter.
Alternately: Kill all 4 members of mixed quartets of stewards and non-stewards so that they will all respawn simultaneously. Eventually, and it was not long for me (about 5 respawns), all 4 will simultaneously respawn as stewards. I soloed this event using this strategy.