1; This will happen whether you have contracts in place or not. You may as well get paid for it. If you deliver to a client who you're not friends with on FB you'd have no idea what they've done anyway.
2; You will do more damage to your brand trying to prosecute contracts with family members for a couple of FB photos than you will just letting it go.
The majority (90%+) of my sales are digital. I only have a passing interest in what happens to them from there provided it's for 'normal' domestic use. They're not watermarked so the realistic chances of my customer doing a horrible edit, posting it online, having someone see said horrible edit and that person actually inquiring as to who the photographer was, making the judgement that it was ME who did the edit, and then having that person actively avoiding my business on that basis is pretty low methinks.
As an aside, I truly believe the "don't sell your files because people will make dodgy prints at Walmart and your reputation will be ruined" mantra is perpetuated by businesses clinging to an outdated business model. Might have worked in 2005 but not now...the world has moved on.