Is it okay for wires at the C terminal to touch?
There's no problem with those wires touching. However, screw terminals are commonly only rated for one or two wires to terminate at them. If you're adding a third, it might be time to use a &quot;pigtail&quot;.
Creating a pigtail

Remove the wires from the screw terminal.
Combine the two wires that previously were under the screw terminal, with the wire you're adding, and a short bit of scrap wire of the same or larger (smaller gauge) size using a twist-on wire connector (or other approved means).
Attach the short bit of wire (pigtail) to the screw terminal.