Mrsdaly - thank you much! I have bus-a-phobia I guess. Always avoided them at WDW, perhaps irrationally. It may be the waiting - don't know. Maybe you're right. We're in the same situation - grandkids are 2 and 4 and my son/DIL are either taking two strollers or using their double (not sure).
We are kind of set on the monorail idea only because it in effect is another attraction for them. So I do think we will go that route the last day (this would be leaving the Dolphin about 3:30-4:00 PM, trying to make it back to Epcot by 8:00PM for Illuminations at 9:00 - we won't at all be picky about where we see it from - in fact the closer to the international gateway the better, even though we'll miss a lot of what happens on the water. We had a spectacular viewpoint one Christmas that to this day - even as I type this - sends a warm feeling throughout. I can't ever imagine topping that - but seeing my grand-girls reaction to the countries lighting up and the lasers etc may well match that.)
We've always driven to MK from the S/D, or Y&BC (we've had 5 WDW trips where we stayed at one of these). We used to drive to GF and take the monrail - before they got strict about parking for non-resort guests there. You are right - the parking lot at MK is a much longer trip (talking two cars, park, get everyone together, tram to the ferry or monorail etc.)
But for the other two trips to MK that we will do in the morning, I think I may try the bus route once.
(The Dolphin is the last resort stop? OK - so it's an express to MK, but potentially full too, right? And then going back, is it the LAST resort stop. I know I could look it up - and I will, Just thinking out loud.)