Ok, I am going to disagree with Peccie on this one.
I disagree that you must "do your best to crack this because it's not joke once you are dealing with sleep issued with an older child"
I also disagree that it is a problem to take a child into bed with you.
As things are, your baby goes to sleep in his own bed and then wakes up during the night and wants to come in with you and your DH. Why is that a problem exactly? Is it because you have been told that this is wrong and unnatural or because it truly is problematic in some way to you? Why does your DH have to leave the bed if your son comes in? Why can't your son just come in between you - babies really don't take that much space and he's old enough now so you don't have any worries about squashing him. Or if you prefer, get a bed rail and put him at one side, you next to him and your DH on the other side.
Most babies want to sleep with their parents. It is natural. You don't see kittens or puppies sleeping away from the parent dogs so why on earth should baby humans be any different. Would it be so wrong to go with the flow a bit more and accommodate your son's needs rather than imposing old fashioned and draconian sleep training onto him. Sleep training will invariably involve your son being distressed and crying - I cannot see how that is good for you or for him.
All my children have slept with me at some point. My DD (15 months) sounds like your DS - she starts in her own bed and then at some point in the night comes in with us. Result - we all get a good night's sleep and everyone is happy. My DH doesn't mind, we still have a healthy sex life and there are no problems at all. Occasionally she sleeps through and as she gets older, the more she starts to sleep through. She will do it in her time with no pressure or "training" from me.
Incidentally, despite co sleeping until the age of 2 plus, both my 7 and 3 year olds sleep very well on their own in their own beds.