Do note that after some recent changes it’s quite safe to shoot directly from behind your brother’s back at someone who is fighting him in melee, so it’s theoretically possible to go full-on range combat and forego melee completely.
What, really? You can no longer hit your bros if you try that?
“Directly” as in “you are hugging the back of your bro and shooting someone who is standing directly front of him (in melee range)” – can’t be 100% certain but I have yet to hit one of my bros this way. If you are not “hugging” them (your archers is 2 or more tiles away) they count as being in the line of fire, as always (the red shield icon will show) and you’re likely to hurt them.
It makes it possible to keep shooting into melee of 1st line if your archer is standing in 2nd line.