Just my tuppence worth, but I would not insulate the breeze block kennel.
Knock the three of them into one and place insulated dog houses in them.
Insulating the whole of the enlarged kennel will not help the dogs.
Their body heat would not be enough to raise the temperature.
But the smaller dog houses would be dry and warmed by the dog himself.
The pup will bunk in with one of the dogs if you are lucky
Best of luck whichever method you use.
nice boxs but cost a fortune out of most peoples price range them boxs silly price