Yes, it's perfect and reasonable.

Yes.

For one day a week, I think that's fine.

This is more than enough notice. Though, I'd just tell them at the end of your next shift...why suffer through one more awkward day than you have to?

Schedule is changing with my primary family and I no longer can help out my 1 day/week family.

Planning to call a day before my shift and offer to work the next 3 shifts and then I'm not available. This essentially gives them 3 full weeks to find someone. Is this enough notice?