At 19 weeks, he's still just a baby, and I certainly wouldn't be expecting him to tell you he needs to go. You need to give him plenty of opportunities to go outside to prevent accidents in the house.
Take him outside at regular intervals, especially after meals, play and sleeps, stay with him and praise him when he goes.
It's also not unusual for adolescent dogs to take a backwards step in housetraining anyway, even without the addition of a new pup to the household, so it's a case of back to basics with Kona too - regular trips out and praise when he does go outside.