Hopefully we can help you with a few tips with walking to heel on and off the lead. Firstly if you have more than one pup, you are better off doing your training one on one with each of your dogs individually. You must learn the dog to be at heel on the lead and inforce the command heel and show them were you want them.
Personally we also use our hand by our side to give them a visual reference to show them were they should be and this also helps them when training for other commands. The secret to training is to get the dog to focus on you, if the dog is looking at you you have its attention, therefore you are more likely to achieve your goal. When the dog is at heel and doing as you want, make a fuss of them as this helps install that they are doing things right . Also dont worry if one of the dogs is picking it up more quickly than the other as this can be quite common and usually they catch up soon. Once you are comfortable with your dogwalking to heel on the lead you can move onto the the next step of walking to heel without a lead. This is probably best tried after the dog has been out for a run so they do not have all the excitable energy.
Firstly put the dog on the lead and make it walk to heel for a short time, then stop and take the lead off. Most important now is to tell the dog heel and start to walk, if the dog makes a move from your side correct it immediatly with the command heel. If the command does not work you should return the dog to the lead and instill that the dog walks to heel again. It is also worth mentioning that you should do your training little but often to stop the dog getting bored or stressed.
Training should be made fun for the dog also, so maybe do five minutes of lead work then give them a retrieve to do as this will keep their minds active, and you are helping your long term goal of training them to begundogs.
You MUST install all the basic commands in your dog before you can move on in your gundog training, thats if you are to get the best from your dog, as it is their natural instinct to hunt game and they can become unruly if you dont have control from the start. No one wants an unruly dog on a shoot as it can be dangerous for the dog and can spoil the proceedings.