You will have to separate them when feeding or you may end up with just one very fat snake. If you have a tropical spices like the Boa Constrictor then the most likely reason might be that the relative humidity is too low. This is when it's eyes will become a blue colour often referred to as Milky. You should try and avoid touching your snake now as it may strike out and bite you by mistake as it's eye sight will be to a minimum. My snake has stopped eating.
Some snake are what is know as problem feeders.
This needn't be a great concern though as most snakes if well feed before can sometimes go for as long as a year without food with little or no problems. Simply don't handle the snake until it resumes it's feeding or limit handling to a minimum. Another reason why a snake will stop eating is again the shedding process. If your snake is about to shed it may not eat. Other reasons could involve the temperature or humidity.