"Feed a man a fish, feed him for a day. Teach a man to fish, feed him for a lifetime."
Gift them a starter DSLR with a kit lens (wide angle) for Christmas. Let them know you're getting too busy to have time, then sometime during the year, either teach them yourself, or spring for a workshop on how to take family portraits.
They find out what else they can do, get GAS*, and they'll be off to the races.
*GAS=Gear Acquisition Syndrome
TFP- Time (their modeling time) For Prints (Digital Edited files with usage rights)
If you're serious, I can give you some tips. If you're interested in booking clients, discretion is MANDATORY. Hire some more mature (think 30's and 40's) professional models who have the skills to convey your message/branding/style in order to build a portfolio of work. Marketing? Relationship sites, catering to the 30's + crowd. Up your retouching game or be prepared to build a relationship with a professional who can provide your style and quality on a consistent basis.
Equipment-wise, in addition to the lighting aspect, I'd consider renting (or purchasing) a 35mm f/1.x lens for it's ability to create bokeh (depth of field), its ability to capture multiple subjects, and its propensity to avoid image distortion.