Is feeding your dogs 2 times a day better than leaving food out all the time?

I have 4 dogs,the youngest is a Pomeranian puppy and she is 6 months old.Our 3 older dogs range from 8-13 years old and we have always left food out for them to graze. The puppy does not gorge herself but potty training is so hard because I never know when she eats so she tends to poo when you are not looking.Would it be to hard on the older dogs to go to a twice a day feeding? I am leaning towards the twice a day feeding.