WHO YOU SHOULD TELL + WHY
The high level of secrecy surrounding an elopement is precisely its biggest draw – no one can commandeer it, try to talk you out of it, or invite themselves to it if they're not aware it's happening. But keeping loved ones in the dark is in their best interests as well. If you tell your sister and no one else, guess who's going to feel slighted when the news comes out? Everybody except for your secret-keeping sister, who, by the way, may not be at all happy to be put in that position. The surprise element is precisely what differentiates elopements from other types of weddings; so if an elopement is what you want, keep your plans under wraps if
If You're Not Engaged
Skipping the engagement phase and going straight to marriage is what elopements were made for. The element of surprise is ironclad and you're not obligated to disclose your plans in advance. If a discussion of your whereabouts during that time period comes up, saying that you'll be traveling and/or on vacation is truthful without revealing your elopement plans.
The exception to this is if one or both of you has non-adult children. Kids need to be prepared in advance for any marriage that involves a parent, and bypassing the adjustment period that an engagement affords is already a precarious situation. Advising young children in advance and including them in your elopement experience is the best-case scenario, but at the very least, they should be informed of your plans in person and given the opportunity to ask any questions before you take the plunge.
If You're Engaged
Once an engagement has been announced, people will naturally begin to question you about wedding plans. If you're considering an elopement from the get-go, simply remaining noncommittal about your future "wedding plans" is your best option.
Sometimes, however, it's the stress of wedding planning already underway that ends up being the impetus for an elopement. The point you are at in the planning process and the corresponding circumstances will help determine if you're obligated to disclose your elopement plans to your parents and/or close family members in advance or not.
If you're only in preliminary planning discussions and no financial investment has been made, you needn't disclose
If you're in the early or mid stages of planning and any monies spent have been your own, you needn't disclose
If you're in the early or mid stages of planning and a small investment of money not your own has been made but can easily be refunded or repaid,
you needn't disclose
If you plan to simply precede the wedding with a private elopement rather than replace it, you needn't disclose
It's when invitations have gone out and/or someone other than yourselves has already made a significant financial investment that a discussion about your newfound desire to elope is essential. Unraveling an event at this point is a complicated matter affecting many people, and those who are immediately involved are entitled to hear your reasons for wanting to replace the wedding with an elopement and discuss the implications before it happens.