Welcome to the forums. What are you plans for arriving and departing (which ferry or plane)? Your two best bets for fishing on a 5 day trip out of Rock Harbor (and returning to Rock Harbor) are Lake Ritchie and/or Chickenbone Lake. Fishing from shore can return successful results, especially at Lake Ritchie. Other lakes on the northeast end have fish but they will be very difficult to reach since none are on designated trails. Off trail travel almost everywhere is usually very rough going. At the top of this subforum there is a sticky post with a chart of lakes. Also, it is easy to search this forum. Use the advanced search button (the little gear icon next to the search box).
Lake Superior fishing, especially from docks or shore, can be fruitful but is typically quite spotty. It also requires a Michigan fishing license. Remember to read the
park rules for fishing regarding restrictions (no barbs on hooks, no live bait, size/species restrictions and control of invasive water fleas.
With only 5 days, you could maximize your time at these 2 lakes by taking the water taxi to Moskey Basin or Chippewa Harbor or McCargoe Cove. This can be a bit pricey for 3 but it will make things more efficient. Lastly, if you plan on staying a night at Chickenbone Lake, then the West campground is by far the more preferred CG vs the East one.
Without a water taxi you will have to cover some miles to get in some decent fishing. If seeing the island is a greater passion than fishing then you could be more flexible (and easier going) with your days but still maybe make it to Lake Ritchie for some fishing time.
If you were more than just kidding about keeping up with your kids, I suggest you consider this itinerary:
Night 1: Daisy Farm or Three Mile
Night 2: Moskey Basin
Night 3: Lake Ritchie (or Moskey Basin again with day trip to Lake Ritchie for lunch and fishing)
Night 4 Daisy Farm
Night 5: Rock Harbor (or Three Mile assuming a 2:45 departure on Queen)
If you are still feeling good after day 4, then I suggest taking the longer route back via the Greenstone Ridge. It has some great views you will otherwise miss.
If you feel serious about 8 to 12 mile days you can try to cover more territory but one good thing about Isle Royale campgrounds is that you can alter your itinerary each day if your hopes and dreams exceed the endurance of your feet. But based on your comments I suggest a softer going approach for your first trip.