Two 20-kg suitcases? That's my regular vacation luggage ;-). I had at least 100 kg of total luggage when I relocated by train in 2008, foolishly thinking "no luggage limits on the train!". It included a 35 kg duffel bag without wheels — it took me 45 minutes to change platforms at København Hovedbanegård. That's what a student budget means (total money spent on 2500 km relocation: <€100).
Having used both 2- and 4-wheel suitcases, I do not recommend 4-wheelers for street use.
I recommend suitcases with big, solid wheels. I use the Eagle Creek Exploration Series ORV Trunk 30. They use skateboard wheels. You can walk with two of them, dragging one behind you in each hand. Their sides will touch each other and you will be rather wide, so be prepared to stop to let others pass. Take enough time, don't be in a rush.
Some have suggested pushing two heavy 4-wheelers in front of you. It may work in airport terminals and hotel lounges. It won't work out in the real world on any tiled pavement. The slightest discontinuity between tiles will make the suitcases tend to fall over forward. Here in England, such discontinuities are many. It may work on a street with smooth tarmac, but even on most streets, there may simply be too much friction, in particular when both are heavily loaded.
The last time I tried to push two 4-wheeled suitcases in front of me on a tiled pavement, I lost one wheel and damaged two others beyond repair. I find that when heavily loaded in the real world, I need to pull the suitcase behind me on 2 wheels anyway, and then a dedicated 2-wheeler with good wheels performs better.