The dicey part is how much equity they get, do they get paid dividends, do they only get anything back if you sell, etc. I am curious to see what others say as far as options and advice go in that respect.
My startup was in a similar situation (although it was a close friend who was investing, not a family member). Our situation was different, as they were expected to come on as a fulltime member of the team as well, but that never panned out (they couldn't put the time in due to other commitments).
So now it's dicey because the percentage given to them was based on $$$ investment + an expectation of day-to-day involvement (which never happened). So now its hard to quantify what their actual ownership is.
So I would advise to make it very cut and dry, and put it in ink (by a lawyer). An example of the chop-up (in layman's terms) could be they get say 7% of ownership for 25k with no other expectations from them other then a check. They get paid if you get sold / acquired or if someone buys their share otherwise they get nothing (no yearly dividends / bonus or profit sharing etc).