HI .. Only advise I can offer is to please
try to keep Willow in a separate place,away
from Popeye & kittens.It's not a natural
situation for cats with kittens to share close quarters with other cats, even if they are related .Hope someone with more experience can help You with this problem. Good Luck to You!!
P.S. Are Willow and Popeye spayed yet??