My suggestion for the first question would be to bring the outside dogs inside, then you wouldn't have to worry about them getting cold, or wet, or overheated. Houston weather is so unpredictable and miserable at times (most of the time) that I, for one second, wouldn't want to live out in it. Would you trade places with your dogs? IMO it's really not fair that they have to live outside while the mini Dachshund gets to live inside with you.

As for the mini Dachshund, I agree with Karen. You should have him vet checked to rule out a medical problem. If he's not neutered, that could be causing a problem because now he's at that sexually mature age where marking becomes a big problem. Like jiena said, try retraining him and get him a litter box. By paper training him you've taught him it's ok to go potty in the house, on the floor. The only difference is there is a pad under him, which doesn't seem to matter now.