<human>: Can you provide a brief rundown of the text in within 3 sentences?

A week and a half ago, I decided to adopt this beautiful little dog, because she was the most calm dog I'd seen in a long time.  While waiting to get the paperwork for her, I was seated next to a kennel that contained her 8-month old puppy.  He was the last one left of the litter that she was picked up with last Summer, and he kept sticking his paw out to scratch her ear.  I asked to see him too, and it became clear that I would do well to take them both.  Here's a picture:

They are still great, and I love them both, but they were not walked or trained, since they had a yard.  Subsequently, I have been somewhat frustrated trying to walk them together while also promoting loose-leash.  I have decided to walk and clicker-train them separate.  I've read quite a bit about strategies, so I try to make the training fun for both.

The problem is that when I try to walk him outside, I provide click-treat incentives to keep moving, but we have never gotten more than 30 feet from my door, because he will sort of shut down, tail between legs, crouching to the ground after a while until I change direction back towards my apartment (and his mother).  He also won't play with me/toys much and will keep coming back to try to rough-house with his mother while I'm petting her.  She doesn't have the energy he does, so if he only plays with her, he ends up with a lot of bottled up energy.

I'm planning on continuing to train them separate, and I know it will take time, but I was wondering if anyone had any tips on dealing with that kind of separation anxiety during the training process.  It's better since I've gotten them separate kennels, but I really don't want him to see training as a negative thing (being taken from his mother)
<bot>: Adopted mother/son pair, son won't walk/play without her, and I want to train them both.