Teaching a dog to fetch and teaching a dog to love playing with toys are two separate, but related things. Since your question title is specifically about toys, I'll answer that one. If you're curious about teaching a retrieve, you can check out this question.
I would recommend doing sessions with the other dogs in another room so as not to disturb him at first. You can add them later as a distraction when he gets better.
What does your dog love to put his teeth on?
When you're first starting to teach a dog to love playing with toys, start with something that he already loves putting his teeth on. It could be anything including things that may not normally be considered "appropriate." Right now we're just focused on fun with things in the mouth. Here are some starter ideas:
- Braided fleece
- Old sock with paper inside
- Twisted up paper bag
- Bungee tug toy
- Chew toy
- Chew bone
- Big ball
Obviously the things that are longer are going to be easier for you, but if your dog doesn't like those then use what works for your dog.
Encourage play with erratic movements.
Now that you've found something he loves, encourage him to play tug with you. Move the toy in erratic shapes so it acts like prey. Rabbits don't move towards dogs so neither should your toy.
Make sure to stop the game if he ever gets you instead of the toy. At this stage he probably doesn't mean it so he should pick up pretty quickly that the goal is the toy. You can also run away from him with the toy, keeping the toy in a straight line so it's easier for him to target.
Continue to work on this in multiple environments until he'll tug on his favorite thing anywhere. Keep the tugs very short (under 5 seconds) so he is always wanting more. If he doesn't have an "out / drop" command, hold the toy very still in a way that doesn't allow him to play with it. As soon as he lets go and offers a control (sit / down / etc.) release him to get the toy again.
Similar toys, same games
Now that he's playing with you and the toy, start introducing new toys with a similar feel. Does he like hard dumbbell type toys? Maybe he likes soft squishy things or things that make funny noises.
Switch up toys and require that he always play with the toy that you have. You don't want him running off with toys (trust me, it's very hard to overcome once they start). Throw a big pile of toys on the ground and ask him to play with the one in your hand. Then drop it and pick up a new one and ask him to play with it instead. Go through a variety of toys. Not only will he learn to love different toys, he'll learn that you always have the most fun ones.
One way to help the dog learn to love toys is to ask them to tug before they do something else. Ask for a quick (5 seconds or less) game of tug, and then run over and do some of the obedience stuff he loves doing.
An important reminder is that once you've started to ask for a tug, don't give up. If you give in, he'll learn he doesn't really have to tug if he doesn't want to. If it takes a really long time, take note that you probably shouldn't have asked for a tug in that situation yet.
Toys and Food
Some dogs just really don't like toys to start. In that case, I recommend trying a very hard jerky type treat or looking into something like a TugIt toy. They are specifically designed for dogs who just want to get at the food by only rewarding for good tugs. The better they tug, the more food they get.
Some of the early retrieve work (under 1 ft in distance) can be done regardless of his love for toys, but once you start adding distance, you'll want to be sure you're using something that he loves enough to get, but not enough to keep. Good luck!