Quintuplets are a group of five. A quartet is a group of four. The quartet usually applies to a group of musicians, singing or otherwise. Quintuplets are when five babies are born at same time; like twins, except that there are five instead of two.
There are many kind of Quartets, but the most famous is a string Quartet, this consists of 2 violis, a viola and a cello.
In a string Quartet the two violins play the soprano and alto vocal...
i think it is pretty much impossible to get them on your own. you would need to have fertility treatments done. also if you mention you want them to your doctor he'll say that it is a very high risk...