I would use dewormer for the runny poo
As for the sneezing, if you are using pine or cedar shavings some chickens can be sensitive to the odor causing sneezing.
I was first told to use cedar, then recomended pine, then read the internet article.
Cedar vs pine. Both give off odors, like pinsol or cedar oder.
I now use Fir shavings which has no odor
and have no sneezing chickens.
I also use poultry powder for flea and lice repellent.
People who recommend the cedar or pine, do it because the smell itself repells fleas and lice. But a sneezing chicken I read is more susceptible to other serious infections, so it's best just to do away with anything like that.
so I would try the 2 things I listed and if that doesnt help then maybe they are sick and need antibiotics.