Is it common for a woman of 56 to have difficulty holding her bladder?

Yes. As women age, the supportinfg structures for the bladder may weaken and cause urinary leakage. This becomes much more pronounced when she has kids; the more kids, the higher the chances of urinary leakage. This typically will result in stress leakage and may also be associated with a vaginal prolapse of the bladder (cystocele), rectum (rectocele), or both. Kegel exercises are helpful to treat.
Very common. Many women have some leaking of urine, especially with coughing or sneezing. You should se a uro-gynecologist if one is available, or discuss it with your gynecologist.
You need a complete. Although many women have difficluty with baldder control the reasons are many. You need to see a urologist for a complete evaluation.