face to face - in person,. but if only two are involved, means about the same thing, if context allows it. (Most common) one to one one on one one and one - nope one by one - nope - means in steps, sequentially, no obvious meaning for conversation

the first option is good.

The first one is correct. The colon is a ration symbol. 1 X 1 is "by". This written way is usually for writing areas/volumes. For an example, 2 X 4 is a short in construction materials for a plank of wood that is 2 in. x 4 in. x 8 ft; 3X2X1 can mean a box that is 3 feet long, with a width of 2 feet and 1 foot high. All depends on context. One by one. Always spelt out. "One by one, the students file into the hall". In mathematics, one to one is written as 1-1 and has a different meaning. A "1-1 correspondence" is called a bijection, written as ↦. In the range of 1 - 26, there is a bijection to the English alphabet.

One on One is the most natural phrase.