Do you have a toboggan or two? You could pull one with each hand if they are all too heavy on one. You can get some great ones with higher sides and even seatbelts for short walks.

I start training my dckids once they are about 18-20 months old and walking well with the backpacks attached to my wrists. Right now I have a 22 month old and a 23 month old who can go really long distances already on that system so that we are ready for winter with safety as my #1 priority because we cross busy streets too.