So my BT lady who only has a single kid has an uneven udder. What I was wondering is whether the smaller side is perhaps emptier because he is taking milk from that side YES or is he taking milk from the larger side that is larger because of the increased demand upon it. It would help to know which side to take more from when I am milking her.
If you feel each quarter (half) of the udder you will feel which one is tighter than the other, the tighter one needs emptying. Even twins often only use on side of the udder and you have to milk out the other. I would be tempted to completely strip out the side he is not using, especially if you want to continue milking once he reduces what he takes.
If he is not going onto the bottle (and it may suit your set-up to leave him with the dam) then I would start stripping out the half he is using once a day too, maybe in the evening. That way you will have a good milk supply going once he is weaned.
This set-up can produce an uneven udder, but unless you are showing her it is probably something you can live with.