My extended family is all here Grenada and we made our first day trip from our villa to Seven Sisters. I wouldn't disagree with much of anything the previous posts but would add the following insights. We were a group of 12 with ages ranging from 12 to 61. This was a self-guided tour with two cars. It was a great adventure all around.
1) Getting there is half the fun/adventure. Having some experience in driving on the left hand side of the road in the 3rd world is definately a plus. Driving on wet, windy, mountain roads with few barriers on the edge in another ‘trip’ all in itself.
2) We too hooked up with Kenny as our self-appointed guide. It turned out to be both a good thing and not so good thing. Kenny was very opinionated and was convinced some the older. Larger people in our group were never going to make it. We showed him. He was very helpful in spots on the trail, helping across challenging rocks, giving advice on where to swim. He tried repeatedly to extract more the $20 we gave him at the end.
3) I would say you need to allow 2 hours in total to get the total experience at the falls and an 2hours in driving time (there and back) allwing for a wrong turn or two.