The past two days my pets health seems to be detioriating. He seems to be struggling for air, gasping and very lethargic, no appetitereally need advice
Can you hold his sides to your ears and see if he's making rattling noises or squeaky noises when he breathes? Get a video, put it on YouTube, then copy and paste the link on here. That'll be easier to help you.
The only genetics you have to worry about is a weaker immune system but a lot of times one sibling will have a weak immune system and other siblings will be fine.