<human>: Could you distill the essence of the text into 1-3 sentences?

My mom has had Topher since he was a year old, he is part chihuahua / part mini dachshund, and has never been trained properly. Since her illness, my mom cannot take care of him and he was either going to me or the pound, probably to be put down. So my husband and I agreed to take him into our tiny apartment. Where, by the way, we already have a part border collie / part Australian Shepard. She's the exact opposite of Topher: house-trained, obedient, and very calm. Together, they have no problems at all with food or toys but Topher changing her. Yesterday, she peed in the house. She hasn't done that since she was 6 weeks old. We are getting complaints from our neighbors that he will bark, howl, and scream all day while my husband and I are at work. Please help us. We really don't want to send him to the pound or anything like that. This was an unexpected thing and we are not financially prepared to send him to a training day camp.
<bot>: Unexpectedly acquired a new dog. He is converting my other dog to his evil ways. How do I go Harry Potter on his Voldemort ass?