Good for you, Kelsie...your group sounds like it's off to a good start. Old standards like the following are good in that even if people don't know all the words they are at least vaguely familiar with them:
On Top of Old Smoky
Frankie and Johnnie
BlueTail Fly
Swing Low, Swt Chariot
Country Roads
The Banks of the Ohio
Aura Lee (Love me tender tune)
Mountain Dew
Druken Sailor
Summertime
Wabash Cannonball

All of these are easy to play, involving only a few chords, if anyone is playing a stringed instrument, and all easy to sing, without straining anybody's range.

Keep us posted how it goes. Your group members may come up with more tunes also, they know and can sing.