chicken loosing feather, plllllz help me am soo worried !!!!!

i have four chickens, age unknown and a year and two months leghorn rooster and they all are loosing their feathers !!!
it started with one losing feather around her nick and on her back so they told me it was because of the rooster 

so i did nothing because i thought it was nothing but three weeks ago when i was bathing my roo i noticed a begging of feather loosing on his chest and step by step the other three chickens began to loos their feather 

my brother in law told me that when the chickens start to loose their feathers it means that they are about to die " i'm really in to those chicken i spend all my day just hanging out with them, especially the rooster i bought him when he was only a day old and he's like my baby he even sleeps in my lap and loves to hugged by me" he completes my life" so if he dies i have no idia what the heck will happen to me .. plllllz tell me it's not true :'( :'(

then i read that it could be molting, but it's summer where i live now, and i read that molting happens only at the begging of the winter !!

note, i've noticed and it's just on the chickens that on some days they become so lazy and they will just go to sleep standing and they won't move around fast and funny like always but on the next day it will all go. and they spend a whole tow weeks without laying a single egg but yesterday only one named Tota laid one and today there was also another egg 

but they eat perfectly and also "get the food out" perfectly in fact they have a very big appetite :) and that's what make'em special :P 

pllz help me with my chickens, they are more than chickens to me "they are everything" and i must help them and you are my way to do it so plllz plllz  help me 

it's the first time i hear that they are not gonna die so THANK YOU :) :) 

and do you have any idia what can i do to stop the mites or lice ?????

i clean their house every week and my brother burn it every two weeks for better sterilization "it doesn't seem to be working i guess" :/ 

and again thx alot for telling me they're not gonna die :) 

i definitely will, the first thing to do tomorrow is to check that :)

are the mites white and very small ????? because i saw few in their water when i was changing it 4 days ago but i thought they fell from the tree !!

thx alot for your answer :) 
i really appreciate your help :) thx alot :D

i don't know actually he just tells me to take my chickens out, and i take them so they can play around until he finishes, but everything will be exactly as i left it 

but i asked before alot of people who raise chickens and they told me that it won't hurt them it will just kill any bacteria in their house and that's why i allow him to do it 

and i will search google now for it :) 
and really really thank you for helping