Congratulations on listening to your instincts and deciding to cosleep. I don't know who told you cosleeping is bad, because is not a "bad" habit to bring your babies into bed with you--it is a "good" habit which actually is a wonderful transition method for your babies from the crib to the toddler bed (unless of course in 12 months you want two 2 year-olds who drive you nuts by climbing out of their cribs all the time--or won't stay in their beds at night).
I think many people feel comfortable for the ten months they are pregnant with their babies, enjoying the closeness...and then once the babies are born, social pressures convince them to insist on seeking distance so as to make the babies independent--but really the more closeness you give your babies, the faster they will gain independence. You've got to listen to your instincts. Your babies still need you.
After a few months of letting your babies sleep in your bed with you whenever they ask, get a couple of "big boy beds" (toddler beds that look like race cars or care bears or something) and set them up in their bedroom. If you are worried about your boys falling out of bed, put just the mattresses on the floor and assemble the rest of the bed once they are a bit older. Make a BIG deal about it as though it's the most exciting thing in the world (i.e., model the behavior of loving a big boy bed). Let your children sleep with you at night and once they are asleep, make sure the baby monitor is on and place each one in their beds with the blankets on them nice and cozy. Closeness with mommy and daddy and the warmth of your bed is truly a wonderful way to ease them into loving their own beds.
By the way, if you read Elaine B.'s request today for advice on her 11 month-old, you can see that babies really do just want to be close physically to their parents while sleeping...and a bed is more comfortable than a crib, and easier for a growing toddler to stretch out in. In other words, it is inevitable that your babies will soon be entering their separation anxiety phase and you can bet they'll get what they need...either now, or a year from now. The good thing is, you can choose to work through this phase now and get it over with so they can get on with growing. Responding to your babies' needs for nighttime closeness now will assure your time with your children when they are 11 months old (and older) will be a lot more satisfying to you and to them. And as for naps, well..I recommend using two baby slings. I've worn two babies at once and it works just fine for naps. Then again, I've been blessed with a strong back so this may not be for everybody. Good luck with everything. I also want to say you are not failing your twins, you are doing a good job with them. Keep up the good work! All we parents can do is try our best!!