2 to 1 is usually written "2:1" and it's either a score for a game like soccer or it means there are twice as many of the first group than the second. It's called a ratio, a mathematical relationship of two of the same kind. Modern TV sets are made only in 16:9 ratio (aspect ratio, in this case). That means that if, for example, the width is 80cm, the height is 45cm (16x5 and 9x5). If you said "2 in 3" or "two out of three" it would mean what you suggested, that in three persons there are two... Note that the ratio is often written as 16x9 not 16:9 although the second one is correct. I don't know about UK, but in the US, if it's 2:4 it should be a ratio and read as "two to four" although the TVs are said to be in a "sixteen by nine" ratio. If it's an actual size, like 2 inches by 4 inches, a standard American size for a piece of building lumber, it's written as "2x4" and read as "two by four".

"2 to 1" means "two" for every "one" - there were twice as many of them as there were of us. Two of them for every one of us. There were two girls for every man. It's not referring to 3.