When my daughters were young [they are grown women now] they were only 2 years apart and very competitive.  To keep them from having to compete for my attention, I alternated one day every weekend to spend with one daughter for our daddy-daughter day.
 
They tease me now about how they tried to trade off those days with each other but they are very close and their relationship with me is great.

Oh, and one other thing......When one of them had a problem with school or in some social thing I never compared one to another as a "good example". That would only have produced animosity between them and as they were completely different people that could only be de-motivating to both.

Elliot