Question 1080385
Your question as typed yields a fractional answer, which is not possible in terms of age. I think you meant to say that Lee's younger sister is three years younger than him not the older sister. 
 

Let x = Lee


Let 2x + 1 = older sister


Let x - 3 = younger sister


The sum of their ages is


x + (2x + 1) + (x - 3) = 26


Solve for x to find Lee's age.