I would recommend you definitely NOT keep just a breeding pair. IMO, that would be a recipe for disaster just waiting to happen and for Murphy's Law to kick in. As you stated with your comments about keeping less than 3 males.
Personally, I don't see a need for 3 Trio's of each variety. As a general rule, I run two lines for each of my breeds. For breeders I will have 4-5 females and 1 male in each line. Additionally I keep one "backup" rooster (brother) in each line but he doesn't get bred unless something happens to the stud. Once I get at least a dozen or so cockerels from that breeding the backup goes to freezer camp or sold. Should something happen where I lose both males in the line I would just use the male from the other line, close the line without the male, and start a brand new line with him.
Now, that said, if you need to run 3 lines for specific reasons, you could always cut down the females by 1 or 2 but I wouldn't go less than 1 stud and 1 backup for each line unless you have too.
Hope that helps. Without knowing more about your lines, what each has and doesn't have, and what your future goals are that's the best I can do.