treat with moxidectin mate i think its the best wormer on the market if you have a strong infestation of worms you will have to do it 2 weeks later after the first treatment as some treatments wont kill the eggs so a second time is a must and with tape worm it could even take a third treatment if the birds could be put in a aviary while been treated it would be perfect if not get out the loft burner and torch the loft after every treatment i still think worms may be your problem also a test for worms wont cost you that much there loads of lads doing it now a lot of fanciers now have there own microscope