If I had to guess, just based on the description, this is at least a three-day job, i.e. 21 hours, billed hourly, because there are so many unknowns that could rack up wasted time. Since it’s for charity, and family is involved, you might elect to do it for free, which gives you a lot more freedom and fewer “issues” later), but even if you do it “pro bono”, you MUST track the hours and compute and deliver a bill using your day rate. (If you have not yet established your hourly and day rate, there are a million threads in this forum that go into excruciating detail – well worth reading on your own time, so I’ll not repeat them here).
Why go to the bother of making up a bill for a Pro Bono job?
So you can mark the bottom of it “comped” or “No charge”.
This has several benefits to you: first, it puts a dollar value on your time and talent. People don’t value our work product if it’s free (“un-earned” in some way), but if they feel like they got a “special deal” on something that ordinarily costs, now they will treat the work product with respect and value it. It’s bizarre, true, but it’s human nature, and you can count on it.
The second benefit is, you are off the hook for change orders and revisions and follow-on work; the delivery with the “virtual” bill represents a completed package with no “strings attached”. You can submit the work as a take-it-or-leave-it proposition, with a clear conscience. If they keep insisting they want more, it’s now your choice to bill actual dollars for the follow-on work, or refuse it. This gets you off the hook with the “family” as well, as there remains no attached obligation for follow-up, which they would also expect to be free, ordinarily.
The third benefit is, others will not be coming to you insisting on the same “freebie” rate. They will know what your time is worth, at the beginning of the negotiations, and that while you have a heart, you’re still a businessperson.