First, forget what your mom and MIL say about their successes. Each child is different.
If you son does not have a sense of the bodily cues and signals, you will be keeping track of time until it happens. This is one of the most fundamental pieces of the 'potty training' puzzle, and believe me, you can't *make* this happen any sooner. It's more to do with their physical development (feeling the urge to go, and then being able to have that feeling *in advance*, to cognitively understand "I need to go" in an anticipatory way, getting to the toilet in time, etc.).
So, you have a couple choices: you can keep on as you are, giving support (because yes, this IS in one part US being 'trained' to get our kid to the toilet in time) OR you can wait.
One somewhat puzzling thing for me is this question: why do you have your son still in diapers if you are wanting to potty train him? The ideal experience is for him to be in training underwear, to wet, and to actually feel the wet on his body. THIS experience is what is informative, and if he's having a diaper catch the pee, there is little impetus for him to want to pay attention to this stuff, to want to learn his body's cues. Why? Because, ultimately, the 'reward' for using the toilet in time is *staying dry*. If you are letting him feel like he's 'dry' instead of having him experience the inconvenience of being wet, I can tell you this will take longer.
So: if you are really ready to dig your heels in and *really* potty train, take that diaper off when you are home. As a nanny and a mom, when I first started with potty training kids, I had them in underwear at home/in the neighborhood and in diapers on outing. They need to know and feel the difference between diapers and underwear. I avoided pull-ups like the plague (too many problems with them-- kids can't truly get 'wet' from accidents, they are like glorified magic underwear because they go on/off like undies but absorb like a diaper, etc.).
For what it's worth, after helping LOADS of kids with potty training over the many years I've worked with little ones, when it came to my own son, I didn't start until he was three, and saw ZERO interest. At three years, four months, I simply told him "well, cloth diapers or cloth underwear, take your pick. No more paper diapers." M., after this, we had about a small handful of accidents and he's been largely successful; he was staying dry all night after two months in underpants during the day. All that to say, despite everyone else's success stories, if you feel like YOU are driving this train and your son isn't interested, it's okay to wait a while. And when you resume, take those diapers/;pull-ups and put them away during daytime/at home hours. Once he really learns his bodily cues and puts together "bodily cues=have to go= must go OR wet pants", he's likely going to sail ahead. But if he's not getting that most important signal from his own body, and not feeling the natural consequence of not using the toilet-- if these two things aren't in place, YOU will continue to be doing the 'training'.
(Sorry-- in short, they aren't ready until they're ready.)
For fun:http://www.mamapedia.com/questions/8907917772613353473