So why do 你 think Mello and Near are named that?

That's a good question. The 作者 说 he wanted it to be a story to where 你 can speculate unmentioned things for yourself.. so, I'm not sure.

Personally, I think they were both meant to be ironic. Mello, like 你 said, is anything but mello. Near, I think his name is ironic because he's distant from everyone around him- but on another hand, it could also mean that he's always "near the target" therefore always figuring things out.

This is all speculation though.

Hmmm...

I think that Mello's Alias is supposed to be ironic, because he's not calm at all.

Also, for Near's Alias, He's smart, and nice, so maybe it means that 你 always want to be near him.

It's confirmed that "Near" comes from taking the two first letters of his name with the two last letters of his lastname and form a word out of them;
(Na)te Riv(er) -> Near

As for Mello, anyone's guess is as good as mine. He could've gotten his name from Anthony de Mello for all I know.