Egg eating

I have two broody hens one's a bantam and a silkie, Five eggs have gone missing two from the silkie and three from the bantam. I found half a shell in the bantam's nest, is she just eating the eggs that are no good or is this going to be a bad habit. I have been putting food in her box, because i have never seen her leave it there is water in the coop.
This is the thirteenth day see started with 10 eggs was this too many? Many thanks

She might be finding it hard to keep so many eggs warm in this cold weather.  She is likely to have eaten any she thought were not viable rather than attract predators.  It is good nutrition for her as well.

Do also check as sparkyrog says that you don't have a vermin problem.

Try and take the food and water out of the coop.  You will know if she has been out to eat and drink as she will poo at the same time.  Broody poo is large and stinky so you can't miss it.  If you leave her in the coop with food and water she is more likely to soil her nest and contaminate her eggs.

The other problem if you have 2 broodies together is that they try to steal each others eggs when off the nest.  This can cause breakages so you are better if they are housed separately.  A rabbit hutch makes a great broody hutch and run.   

Don't put her in with a hen and chicks as they would fight.

I have moved broodies and eggs to a rabbit hutch twice before and they were fine both times.  Their instinct to sit is very strong.  It might help if you could put some sort of a partition between the 2 broodies so they can't see each others nest.  Good luck.