Private citizens are not bound by "selective enforcement." That's a legal term for governments. I can selectively enforce my right to allow certain people on my property and ban others as trespassing. I can selectively enforce my copyrights on artwork and articles such that certain people may make copies for personal use while others cannot, based solely on how I'm feeling that day. And, I can selectively enforce my right to force you to abide by our contract, although I can't selectively enforce my obligation to you.
One exception on selective enforcement is protected categories (race, sex, religion, etc). You can't exclude people based on those things, or based on things that apply almost exclusively to those things. Being the parents of a military member, or even being in the military, is not a protected category.
