I think that Edward treated Seth and well, maybe not Leah so much, just fine.
Edward and Seth really became friends, brothers almost in Breaking Dawn. They joke together and talk and even sit near each other. When Bella was pregnant, he confided with Seth before even Jacob. (Remember how Jake was getting the info about her condition from him?)
Leah and Edward never really had a relationship, save the fact of him threatening her if she hurt Bella (verbally or physically) again and yelling at her when she yelled at Bella on Jake's behalf. Leah never tried to console Edward, or even talk to him. She rarely entered the Cullen house unless it was an extreme situation or Jake asked her to. Even then, she was out of there fast. I have no evidence or reason to believe that Edward and Leah even talked besides the threatening thing and never about anything other than formal pleasantries.