I seriously need your help with this. Is it possible for a group to consist of only one item? If you ask me, it's impossible because there has to be at least two items. Please guide me.

1 : two or more figures forming a complete unit in a composition
2 a : a number of individuals assembled together or having some unifying relationship b : an assemblage of objects regarded as a unit c (1) : a military unit consisting of a headquarters and attached battalions (2) : a unit of the United States Air Force higher than a squadron and lower than a wing
3 a : an assemblage of related organisms — often used to avoid taxonomic connotations when the kind or degree of relationship is not clearly defined b (1) : two or more atoms joined together or sometimes a single atom forming part of a molecule; especially : FUNCTIONAL GROUP a methyl group (2) : an assemblage of elements forming one of the vertical columns of the periodic table c : a stratigraphic division comprising rocks deposited during an era
4 : a mathematical set that is closed under a binary associative operation, contains an identity element, and has an inverse for every element
[M-W's Col. Dic.]

I agree with you.
Of course, sometimes people use words very casually and loosely.

I wouldn't use the word without at least three in the group.