In terms of time efficiency, I don't think Yeosemite and Grand canyon are a good combination. Especially during April.
In April, you're mostly limited to the valley. Several hot sites are still not open yet, such glacier point, Tioga road. You can still access to a lot of picturesque points though.
Consider Gran canyon only, but extend it to cover the grand circle. That's a bout a good trip for 9 days. The Grand circle covers Las Vegas, Grand canyon south rim (noth rim is likely not opened yet), Monument Valley, Canyon land NP, Arch NP, then turn back to cover the Bryce canyon, Zion NP, etc. There are a lot of place no less than the sites mentioned above.
I bet although this itinary missing the Yosemite NP, your brother would still think 9 days are too short for the circle. You really urr, ..., 90 days.
If Grand circle is too much for you, consider a mini version which covers Zion NP, Bryce Canyon, Grand Canyon(and add dots between them).
Get some exercise before the trip. The best photography are usually somewhere need a little hiking. Don't just hop on and off the car.
Oh, by the way, remember to carry cramp-on (get it from REI) for each person. A lot trails could be still slippery, if not icy.