How to have Craft 3 and 2 on same host?
Both the craft/ folder name in Craft 2, and the craft executable in Craft 3, can be renamed.

Since the craft executable is user-facing (when SSH’d in), I’d recommend leaving that alone and rename your craft/ folder to something else, maybe craft2/. Then in public_html/index.php, update your $craftPath variable to point to the new location:

$craftPath = '../craft2';