ok a few weeks ago the oldest chicken we have died ( with a bit of help ) she was 8 yrs old. she went down hill pretty quick & we just thought its old age she didnt wanna go into the coop at nite & during the day would eat & drink & walk around a bit but not with the others. she would mostly go to a quiet place & just stand there huddled up. a few days after that we put her out of her misery. but noticed she was quite swollen underneath. last week had a light sussex 1 yr old was laying soft shelled eggs & 1 day didnt get rid of the soft shell only the insides 2 days later was very sick & we managed to get the soft shell out but she died a few hrs later. now i have a shaver 1 yr old who is showing same symtoms as 1st chicken that died, standing huddled up swollen underbelly & she is missing a few feathers around the side of her butt. are these 3 the same & if so its obviously contagious. what can i do to save the rest?