Trouble in the world of puppy

Two of the puppies, Afrodite and Apollo, are not gaining weight as they should and they are not as strong as the others. We need to keep a VERY close eye on them. Mum and I were trying to give them some puppy formula with a bottle, but they just made faces and spit it out again. I guess they don't like it. :( Darn. There's enough to worry about with the 6 of them...