I just have to chime in on this one.
For the past 15 years I have owned 4 Dobermans--3 raised from puppies and one adult female rescue. They were (are) fantastic dogs--very much like Shelties in their intelligence, intuitiveness and obedience. Sadly, I have only one now (Big Dee); the other three passed from medical problems (bloat) and old age.
When my soul-mate, Leather Marie, passed this April, I knew I had to have another dog. I'm retired now so home all day. Figured I could manage a pup. Criteria for selection: 1) high intelligence and 2) smaller size. I wanted similar brains in a smaller package. This old boy is getting up there, and managing a 100 pound Dobie in her old age can be a challenge.
Anyway, "Gus", my blue merle Sheltie, is now 14 weeks old and I swear Leather Marie is re-born is this little guy. Smart as a whip and good as gold. Big Dee loves him but I'm cautious because of her size and watch the two of them constantly when they're together.
On Memorial day weekend, my son asked If I would dog-sit his two Shih Tzus. Two more untrained, yappy, crazy dogs you've never seen. Add those two to the mix of Big Dee and the new pup and I thought I would lose my mind over three days. They never shut up, wouldn't come when called, and were generally a royal pain in my arse.
My biggest fear is that Gus would emulate their constant yapping and misbehavior. Here I am trying my best to instill some basic obedience in the pup (especially "quiet!") and I'm working against the tide.
Anyway, when he came to pick his two up, I gently suggested he consider some basic obedience training. Didn't go over well, but, hey, he's my kid. But here's the best: the very next weekend, he was called away on a business trip and asked me again if I would watch his dogs. I declined. As I explained, I'm trying to break in a new puppy here and devoting a lot of time and attention to training. I don't need bad influences at this point and, frankly, his dogs are out of control. He may be willing to live with unruly pets, but I'm not.
Long story short: he boarded them. My son is fine with my feedback (no hard feelings) and he admits they're out of control but it doesn't bother him. I'm ok with that in his house, but not on my turf!
All of this said, I don't have an easy solution for you either, especially since you're in your parents' house. I would suggest some training, though. Perhaps you could offer to arrange that and get your Dad involved in the fun. In any case, I would continue your own training for your dog, and accept the fact that good advice isn't always well received or taken.