Westinghouse and other appliance manufacturers refer to a Fridge and Freezer combination as a "pigeon pair" -- because pigeons are traditionally bred in pairs*:

Frost free pigeon pair, Fridge (RP372V) and Freezer (FJ302V)

* Actually, that sounds self-evident, doesn't it, B-Y? How else would they be bred except "in pairs"? But it seems most people who acquire pigeons acquire them for breeding purposes, and, therefore, "mated pairs" are more desirable than random pairs because their success at mating and producing offspring has already been established.

Some breeders feel it is best to start out with mated pairs of pigeons and doves, preferably not over three years old, that have proven themselves to be reliable breeders and feeders.

http://www.gamebird.com/dove.html

Applying the same logic to a human couple whose two children are described as a "pigeon pair", it would mean that the parents planned to have 2 children [not just one or more than two], probably to replace themselves on the planet -- in the expectation that their "pigeon pair" would produce another "pigeon pair" and so continue the family line from one generation to the next, ad infinitem.

Taking this logic one step further, a couple who has two children by happenstance, not design, would not have a "pigeon pair". They would just have a pair. :)

Of course, this doesn't explain why Westinghouse calls their Fridge and Freezer combination a "pigeon pair". That combination can't mate. They can't even make any heat together. :)