Without seeing a vet it is hard to say what happened however it sounds as if your hamster had either a prolapse of the bowel probably caused by wet tail or possibly a stuck pup as she may have been pregnant if kept with a male and had delivery difficulties.
Not going on the wheel would be a sign of illness and she was clearly unwell.
Ants will appear near a dead animal looking for food.
If the other hamster is ill and he will likely have wet tail if he has been near the female and she had it then you MUST see a vet though the chances of survival are slim. If he is very ill and you cannot afford to have treatment or time to nurse him then ask the vet if it would be best to give him rest
The food does not sound like it would cause this.
I would strongly advise you not to get any more pets because if your house has an infestation of ants and the chance of rats being in contact with you and your animals then it is not a safe environment for them. Rats carry many horrid diseases that can affect people and hamsters.
The place you got the hamsters from may not be the best and the animals may be unhealthy.
Which country are you in? I am guessing not the UK? I would advise you to see a vet very quickly for the male to have any chance of recovery.