As hatchlings that would be fine. Unfortunately turtles grow 4 inches in the first year alone so that 55 gallon tank wouldn't work out for long. However, if you only got one turtle that would be a decent tank for a few years. Even a mature turtle (4 inches) would be happy for a few years. As you've probably read elsewhere on this site, turtles don't need companions in the tank, they're very happy living solo, so don't worry about your turtle being lonely.
I'd stick with one turtle and give him a great set up rather than having two in a less than ideal situation.
Nice work on doing the research beforehand

It will save you a lot of money and stress in the future.