Answer:
During the 1800's these turned women into hourglasses and is becoming more popular again these days
You must keep this thing. Its loss will affect your brothers. For once yours is lost, it will soon be lost by others.
Different lights do make me strange, thus into different sizes I will change.
Left to right Iβm quite bright. Right to left I might bite.
A mighty weapon in the war against winged household pests.
If itβs information you seek, come and see me. If itβs pairs of letters you need, I have consecutively three. What am I?