I can only provide my opinion and (so far) experience about that. I have son (almost 4) and a daughter (15 months), and both sleep fine. I can't say how much depends on their characters, genetics, etc. But nevertheless, one advice that I have read, that we followed, and turned out quite successful for us:
Never take your child in your bed.
In the very first month up to three months, it might help, but for us, starting from 4 months on, it was very rare. From 6 months on they were sleeping in their own room.
If they wake up crying during the night, you go to their bed, try to tranquilize them. When they are very young, most of the time just seeing you or hearing you is enough. Maybe stay a bit until they calm down. If that really does not work, take them in your arms. And if they need to eat something or so, do provide, of course. But try as best as you can NOT to bring them in your bed. Your bed is yours and his bed is his. He has to learn to separate individuals and the space of each and everyone.
On a related note, I once read a book about what is the importance of the father in the first months/years of life of their children. Babyies are born with a feeling that they and their mother form a single entity. The fathers are there to cut the tie (cut the cord is, in that sense very symbolic), and help the child to learn a conscience of self. By bringing your child in your bed, you are slowing that learning.
Now, back to your case, I don't think (not an expert, remember), that your son has any mental health issue. But if they can stay with their beloved parents, they will. I know quite a few children who do that. Now, how to go from where you stand? I would recommend the following steps
- Explain (he will eventually understand), that he has to sleep in his bed, and that his parents sleep in theirs.
- Make sure he has enough to eat at dinners. I know some parents who always stop their child before he was full. That doesn't help children to sleep too well.
- When he wakes up, go to him, talk to him, and possibly stay with him until he falls asleep again, but do not let him in your bed.
- I would expect that the previous steps are enough, but you might want to limit his food intake in the middle of the night: provide less progressively so that he looses the custom to eat at those hours. Consider replacing milk with water. But it has to be progressive, right now, his body is used to a night intake of food.
- Be patient and be consistent. If the rules change all the time it will destabilize the child's routine.
This will not be done in two days, I can guarantee. To change a habit, you need at least a few weeks, and it can quite easily stretch for two months. So that won't solve your immediate problems of strained work and relationships, but it will eventually solve that part of it.
And for the relationship part, my suggestion is that you sit down together and decide together on the best course to follow.
A note on the TV part that appears in the comments. We are very relaxed about that, having ourselves watched much TV in our days (and still do). It might not help, but that is certainly not the only factor for the sleepless nights.
