Welcome to the BYC flock! We are glad you joined us!
Could be a lot of reasons... molt, stress, decrease in daylight, nutritional deficits, age, etc. You may also want to rethink having so many roosters with only 8 hens. Standard recommendations are 1 rooster for every 10 hens. Having more roosters can be stressful to your hens and lead to them getting overbred which can cause physical and psychological issues (i.e. stress) which can certainly impact rate of lay.
Well, in winter they generally don't lay as well. As the light changes and it gets colder, their laying decreases. Somettimes keeping a light on in their living quarters later into the evening (not all night) will encourage them to lay, but I don't like to do that, I think it's good to let them have a break, as nature intended. Also, something could be stealing the eggs, or they could be eating the eggs themselves. Sometimes they will do that if they are bored. Make sure they have things to keep them entertained, even chickens like toys and it's easy to make them stuff to keep them entertained.
Welcome to BYC. Glad you decided to join our flock. The other members have given you some good advice. I would strongly advise removing two of your roosters from the flock. The recommended ratio of roosters to hens is 1 rooster for every 10 hens. As they mature physically and their hormones kick in, too many roosters will become very hard physically on your hens, over-breeding them, biting and plucking the feathers from their necks and backs, battering them, and potentially, seriously injuring them. And even before they reach the point of injury, hens stressed by over-breeding have a drop off in egg production. The only reason you really need a rooster is to fertilize eggs for hatching and 1 rooster can easily handle 10-15 hens in that regard. Please feel free to ask any questions you may have. We are here to help in any way we can. Cheers.