health insurance for step children

my 2 boys from a prior marriage, which i have full costody of, live with my husband and our 2 boys we had together. my x is self employed and has crap for insurance and one of our sons has costly meds, which consequently makes the overages we have to split very high. i would like to add the boys to my husbands policy through his work since i checked his meds and they are about 70% cheaper. i would be willing to have the decree changed IF i could be sure the insurance through his work would cover it, but no one can tell me (his work or insurance co.) if this change would suffice...."just submit the paperwork and we'll see what we can do". If they won't cover it, I surely don't want to change the decree. Does anyone know if there is a standard in the health insurance world regarding the coverage of step-children?