I have a balanced translocation of chromosomes 11 and 15. what are the chances that my mother/father/ or any of my 5 siblings have it?

Genetics: Not enough information to calculate probabilities , but your siblings have a chance to have it as one or both of your parents.

Probably unlikely: In theory, you can come by this 3 ways.A new balanced event in your mothers egg during formation, at conception with dads balanced pattern or at conception with mom's. If you have 5 sibs & mom had no miscarriages the chances are yours was a new event. Studies can be done on the parents to see if either has it.If one does then studying your sibs would be reasonable.