Personally I'm not a fan of Asher, but it seems really popular on this board. I'm also not a fan of Levi.
I like Nolan, Evan and Garrett.
I think Ethan and Nolan make a great sibset. Although then if you have a third I would feel like you started a trend and would have to name the third with an -an.
Ethan and Evan, again very cute but you are staring an E trend.
Ethan and Garrett sound really good together without the trend.
I'm actually a fan of 'trending' names (unlike lots of people on this board), but then I fully believe you have to stick with it throughout all sibset.