My guess is that that they are getting into something that you are not aware of. Maybe put them on a short leash when you are at home so that they are always by your side so that you can see what they are up to at all times for a few days and see how that goes. When you are not home maybe you can put them in an x-pen. This way they still have a play area but it are confined and they can't get into anything like walls or paper or carpet. You'd be amazed what these little guys can get into when you aren't looking. And the effects can last days sometimes... One time Annie got into the bookcase and tore off the cover on a book. She had the nastiest mucous diarhea for a week. Sometimes she just random vomits (probably cause she ate something she shouldn't have) Plus you have two little puppies ! So that's TWO TIMES THE TROUBLE
They're probably playing follow the leader!