I'm sorry, what do you mean by "firefighting"?

He's left alone from 8 am until about 5:30 pm. I take him out every morning around 7:15 before I leave and he always goes pee, and most of the time poop, too. Going is usually not an issue. Also, my sister is home Thursdays and Fridays with him, but she says that she'll take him outside where he'll pee, but then he'll come back inside and pee again on the hardwood. That's confusing to me. When he was tiny, I learned that puppies would go, but would usually have to go again 15 minutes later, but now that he's older I don't think this is the case.

That is a very long time, I don't think I'd leave an adult that long without access to the outside, and puppies need a lot of stimulation and attention. You can't expect him to just lie down and wake up when you come home and nothing to have happened. I mean if you left an 8 month old child alone that long they would have also left a trail of damage. I really don't think that is the right situation for a puppy to be in.
When he goes on the hardwood is it always in the same place, probably where a cat has been actually. Maybe she could have a pad in the place he normally goes and start with him that way

Hi, yes, seems to always be in the same place. I don't think that spot has ever been soiled by a cat. Like you said, you can tell dog pee from cat pee and this is definitely too diluted to be cat pee. However, it's right near their litter boxes.

Also, he seems to be a high-energy, very active breed. My sister works at a dog daycare and after becoming familiar with his personality, I agree that allowing him to be more active would be more fair to him. So she's going to start taking him with her to work 2 times a week. She took him last week from 8-5 and it was the only time I'd ever seen him completely wiped out by the time I got home. He seemed to really enjoy it!

Getting yourself an active breed puppy and then leaving him home alone wasn't really the best thing to do, and I would say getting him in doggy day care is the way forward. Start putting the puppy pad ( I put them on old newspapers) where he tends to go, the smell from the litter boxes will be encouraging him to go near them. Any chance the litter trays could be moved to near the outside door and getting the cats to go out more

The stray that we took in had a litter of 10 puppies and I just fell in love with him! I had no idea he'd be so hyper! I love him to death but he's not easy! And I have put a puppy pad down where I was finding the pee, and then I think a cat peed on it, not him. It's hard to tell who's peeing sometimes.

Also, do you mean actually put the litter boxes outside, or keep them inside near the door? We have a front door and a back door to the patio, which is where the litter boxes sit. The cats have only ever been indoor cats. But we're boarding them soon, so I'm hoping this fixes the problem. However, I worry for when I take my 2 cats back with my dog.

Personally I'd be putting the litter trays outside, but thats because I can't stand the smell of anything like that.
I don't think its practicable to have all these animals inside for the majority of the day, so if you could get your cats to go out it would be a start, and maybe getting the puppy into daycare would be another step in the right direction
You did a very kind and good thing taking in the poor dog and also looking after 10 puppies when you had no experience, its hard work when you know what needs to be done never mind when you're flying by the seat of your pants.
That puppy will need to be taken to training classes and learn whats expected of him and you will need to learn how to work with him and build a team

Yea, the ammonia can be overwhelming, especially with 4 of them. It's hard to keep up. I'd love to let them outside, but the problem is we have no cat door, so they'd have to be let out all day. And technically, the apartment does not want out door cats. And I worry that they'd hop the fence to the neighbors yards.

Actually my brother and his gf raised them all. And you're right, they had no idea what they were doing and the puppies seemed to have turned out, for the most part They kept one and my parents have the mom. The rest were adopted out through a rescue to good homes

I have taken him to training, but it was more of a social since I did it when he was like 4 months old. I'm planning to start obedience at Zoom Room-I agree, he needs training and so do I! The cats will be boarding with someone soon, so I'm hoping this problem will go away, plus the day care for him...

By training I mean go to regular classes and practice every day, I don't mean for hours, just 10 minutes and then do something else, don't do enough for him to get bored. Sit, down, stand and recall then you build on that.
Don't know what to suggest about the cats, I'm amazed your landlord hasn't got upset about the smell, its not going to be easy to get rid of like I've already said

That's ok, the cats have their own forum, but unfortunately they tie into the problem I'm having with my dog. The landlord doesn't know about the smell since we just moved in-they haven't been back for any reason. But you're right, they ruined the last place and we payed a lot in damages.

I think if you solve the cat problem, the puppy situation will be controllable. You're lucky the landlord hasn't yet discovered what has happened, I think if and when (its only a matter of time) you may be looking for a new home. So all in all you sort it out now, or end up in a situation where you are homeless with animals that are more than contributing to it