Twin Toddlers

Hi everyone, need some advice on my twin dilemma!
I have 3 year old twin boys and a baby (under 1). We live in a 2nd floor flat and so getting out the house is pretty much not happening unless I have an extra pair of hands to help. DH works every weekday. I'm not allowed to keep the baby's buggy downstairs.
My original plan was to have the double buggy and a carrier for baby. He is a chunky baby! And grew out of the carrier within months. He also is too heavy for my back to carry and push the double pram.
I got rid of the double and bought a single, however, I need to start getting my twin boys out, there's only so much entertaining they have indoors and it doesn't feel fair to keep them in so much. I want them to start a nursery group this year. They are too naughty to control on reins, I tried and it was a disaster!
Anyone got any suggestions? Are there any buggy boards that would fit both the boys on? Not sure they exist...
Thanks