help advice parastop

treating my pigeons with parastop for a week now as i have samanella . two old hens died of it . i had eight eggs two never hatched two had to be put to sleep because of joints swollen up , so i was left with three as i promised two to another fancier .At this time i have and old hen with a lump on its wing joint and in poor shape also an old cock bird has been retching and a young one this morning . PMV my pigeons , treat them with 4+1 also had my droppings checked clean out every day and change water . honestly dont know what to do or where to turn this is torture.. thank you