And hanging out here really makes having two seem quite logical. . .
At first I would supervise any play very carefully. We configured the pen so that the dogs were side-by-side and that gave them time to adjust to being in proximity with each other. Because our older dog (she was just under a year when we brought in her sister) is a loud, active pup, we had to discern what growls were play and which were truly "get out of my face." Over a few weeks they seem to have reached an agreement and do pretty well.
Others will know MUCH more, but congratulations! They are just too cute!