Here are our options as I see them.

These are in no particular order:

Option 1: Hermit Trail

Stay on river for 2 nights (Hermit Falls-BM8, Granite Falls-BL8) and at 3500 feet for 2 nights (Indian Garden and  Horn Creek-BL4), one night on Tonto Trail (approx 3500 feet).

Good: New territory to cover, less traveled, likely quiet river camping

Bad: Hermit Trail isn't as well maintained, significantly more miles to cover, filter water for 3 days with no available water on night 3, so we'd have to carry plenty. Moving every day.

Here's the word from NPS on Hermit Trail: The Hermit Trail has less snow and ice than any other trail on the South Rim. This is due in part to the trailhead being at less than 7000ft. In addition, at about 0.5 miles the trail turns from north-facing to southwest-facing as it descends through the Coconino Sandstone. So expect some snow and ice at first, but with quickly improving conditions as you descend.

Day1: 9.7mi-Hermit Falls-BM8

Day2: 5.6mi-Granite Falls-BL8

Day3: 9.8mi-Horn Creek-BL4

Day4: 7mi-Indian Garden

Day5: 9.5mi-Hike out

Total miles: covered (without side hikes): 41.6mi

Map:

Part 1
Part 2

Option 2: Hermit Trail

Stay on river first night, one night on Tonto Trail (approx 3500 feet), then two nights at Bright Angel Campground and out. Similar to Option 1, but only on river before Bright Angel Campground.

Good: A good combination of old & new. Three nights on the river, one day to do nothing, or day hike etc.

Bad: Hermit Trail isn't as well maintained, significantly more miles to cover, filter water for 2 days with no available water on night 2, so we'd have to carry plenty until we hit the river again Day 3.

Day1: 10.3 mi-Granite Falls-BL8

Day2: 9.8mi-Horn Creek-BL4

Day3: 9.9mi-Phantom Ranch

Day4: Phantom Ranch-Day hike or nothing.

Day5: 9.5mi-Hike out

Total miles: covered (without side hikes): 39.5mi

Maps: 

Part 1
Part 2

Option 3: S. Kaibab to Bright Angel Campground

Camp @ Bright Angel Camp for 3 nights, day hikes etc. Live in relative comfort (bathrooms, running water,  fewer miles etc). Camp at Indian Garden for night 4 and out the next morning.

Good: Maintained trail, heavily traveled, water available, fewer miles to cover, more relaxing trip

Bad: Same terrain we've covered

Day1: 7 mi-Phantom Ranch

Day2: Phantom Ranch, Day hike

Day3: -Phantom Ranch, Day hike

Day4: 4.7mi-Indian Garden

Day5: 4.9mi -Hike out

Total miles: covered (without side hikes): 16.6mi

Map