I know my method is going to make people cringe, however hear me out:
Let's say you are making for ten people, put ten cups out then pour the water first.
Gently place a bag atop the water and have it naturally float down, in each of the cups.
You'll be able to see the oils, tannins, etc. slowly seeping out of the teabag and gather at the bottom of each cup. This provides a good visual indicator of the brewing.

Once there is a dark layer covering the bottom of the cups, usually takes 1-2 minutes or so, give them all a stir, remove the teabags, then apply the sugar as needed to all cups, then the milk to all cups.

Makes it quick and efficient, rather than dealing with a cup at a time. Also every cup will have been brewed for the same intensity too, no randomly weak cups!