Court-ordered insurance for spouse’s children?

The simple answer is YES your stepchildren will be able to be covered by your FEHB family coverage. As a result of the Affordable Care Act, not the court order, children are covered under their parent’s FEHB health plan’s Self and Family enrollment until age 26. Here is a partial excerpt from Benefits Administrator Letter 10-201, https://www.opm.gov/retirement-services/publications-forms/benefits-administration-letters/2010/10-201.pdf
“Allows married children to be covered; removes residency requirements; removes dependency requirements; and does not require children to be students or have prior or current insurance coverage to be placed on their parent’s Self and Family enrollment. This provision is effective on January 1, 2011.”