@snowsk8er - depending on the thickness of the wires two of them may fit into one of the C(ommon) terminals on the Rachio.
Or you can wire-nut two or three of the wires together along with a pigtail (short piece of wire) and insert the pigtail into the C(ommon) terminal on the Rachio.
So either option works. I’d recommend using wire-nut to join all three common wires together and then connecting that bundle with a pigtail to one C(ommon) terminal on the Rachio, as it may be easier to remove one wire from the terminal rather than two.