Regarding the marking in the house. +1 on what Tanza said. I have 2 intact males in my house - Brando who is 5yo (that came to my house at 2yo), and now Ozzy, a 6mo puppy. Neither has ever marked in the house. And Brando never marked in the house when my youngest b-girl, Liyah, was in heat last year. Now marking the yard, whole different story. The girls mark over each other and Liyah also marks over the boys :rolleyes:. Brando marks over all of them - especially Ozzy.
My 5yo basenjis, Ruby & Brando, were retired show dogs when I got them at 2yo. I had no difficulty in teaching them anything I wanted them to learn (sit, down, stay, etc…). I still do some training with them every day. A couple pluses were they came leash & crate trained.
Any new dog you bring into a house (be it a puppy or adult) will need time to adjust and may fall back in house training, etc. so there will most likely be some retraining necessary anyway. IMHO, it really all hinges upon how consistent you are with the things you want them to do and learn.
Oh, and regarding walking 2 - I had no problem ever walking Ruby & Brando - as they were already well leash trained. Does that mean they don't ever pull? No - all bets are off if a rabbit or deer crosses the road. Could I train them better for those instances, yes. Also, I don't require my dogs to walk perfectly by my side - they are allowed to be out in front if they aren't pulling. One thing I typically do is let my b-kids run in the yard for about 10 or 15 minutes before I take them for a walk. That way, they burn up some energy before we go for a walk.
If you already have a puller, I would work with the puller separately - sinbaje is right about checking out that link or doing a search - also, lots of good books on training out there. My youngest b-girl (1.5yo juvenile delinquent) can be a puller. I would typically take her for a separate walk (a training walk), before I would take her with the adults on a walk. With Liyah, I have taken an hour to do 2 miles before because I would not let her pull. But then I would come back, get the adults and would walk all 3 together - with regular leads (and martingale collars). Really did wonders doing the training walk first. When Liyah joined the other 2, Liyah would be allowed to be up front with the adults if she didn't pull - if she did pull, she would have to walk beside me. She definitely would catch on.