New member and a question about chickens

Hello, I'm new to this forum. My name is Mindy I have 5 laying hens and 1 rooster. We live in Vermont so it does get cold here. They have a coop they get in at night they have a run. My laying hens are 1 barred rock 1 Rhode Island red 1 orp 2 Bramas. Recently I've had 1 of my Rhode Island reds pass and today my white silkie passed. My road Island Road was really lethargic her comb was pale so I brought her inside and she laid down and she started spazzing and then she passed. My white silky this morning was in one of the nesting boxes dead, it looks like she had the same thing happened to her but she had seemed fine the days before. Has anybody have this happen to them and what should I do

 

Everyone else seems happy and mouthy as usual and happy to see me if I have something for them thanks for the input. Couple people have asked me if they are cold it may be possible but I had 4 birds last winter and it was a lot worse and they survived the winter I did light them when it was in the negatives.