He leaves minimal men in W.Europe and S. Europe because he has overwhelming force the next turn to get it back so he realisticly don’t lose money. Me and my bro tried to land UK in Western E/ than fly 6 fighters(U.S) and some of their ground units to stop Germany from retaking it.
Then I feel it is quite feasible to beat your uncle if all he does is build mainly tanks + 1 fighter here and there. What you’re going to want to do is take out his navy and take Norway with the UK on the first round, provided he doesn’t have his fighters within range to kill your navy. After Norway is taken, just keep landing as much as you can in W. Europe. This will take the pressure off of Russia in a jiffy. He can’t use his 8 tanks per turn both to take W. Europe back as well as invade Russia. At first the landings may seem ineffectual since it’s just the UK, but after a few turns the landings grow substantial because of the US, and it should no longer be economical for him to retake W. Europe. After that, S. Europe falls, and things collapse for the Germans.
If you can’t land in W. Europe, then just take it slow and mass troops in Karelia to protect the Russian’s northern flank until the US comes. A joint defense of Russia and UK together should be more than enough to stop the Germans from taking Moscow. Once you’re ready then march towards Germany with masses of troops.