There is no set time for bladder control,it just depends on if the bladder grows at the same rate as their bodies,there are some that do not grow at this rate and can take up to a few years,into their teens before it grows enough to hold all that the body produces.
My first advice is to have them checked by their doctor for diabetes and bladder size.
You can also buy a dozen or so pairs of plastic pants for when you go out,they may not hold to much urine,but may just be the incentive for them to try harder to get to the potty.
I hope this helps.
eviestar, Hi and welcome to the Toilet Teaching board.
There is no set age for gaining bladder control. With my first DS, the first day that we started potty training which was after lunch when his potty arrived in the mail he went to the potty 35+ times. When they wear the diaper then will go a little at a time, so it takes some time to transition to that. Each day the number of times was less. It is normal for the first week or so for a child to go a higher number of times. If you are concerned you can call the pediatrician and talk to one of the nurses and see what they think. Please keep us updated on your twins progress.