Who gets to decide which things have to be an exact match, like roof shingles, and which things don't anymore, like kitchen chairs?

I'm thinking about slightly enlarging my 5x7 hall bathroom, and making it multigenerational, and it would be best if I could fit two sinks in there. The only arrangement I ever see is two perfectly matched sinks, but I am afraid to lose the counter space for contacts and curling irons and such. Have you ever seen a tiny second sink squeezed in? One for full duty jobs like washing whatever, and a second one just for teeth and hands, when needed? Or even a choice of lower/higher sinks? Siblings rather than identical twins?