Unless you use a Power 4 enchanted bow, skeletons are litterally invincible against a regular bow or crossbow, even with arrows of harming or poison.
MCPE-87402
Skeletons are unbeatable with a bow
Resolved
Cannot Reproduce
0
arrows of harming don’t deal damage to the skeleton because it is a dead mob it heals it. Arrows of poison deal damage to the skeleton but when it is on half a heart it stops dealing damage to the skeleton. I don’t know the normal arrows they should kill the skeletons easily.