We just did that trip. Wife and I each had less than 50lb checked bags. I carried a Dry Bag backpack and wife had large carry on and oversized purse. No additional charges.

One note, did have our flight down cancelled about 3 weeks before the flight. Their options for re-scheduling were slim and didn't work for us so we opted for the credit and booked a Cape Air to get there. Price was higher but we had some CC points.

Flight back on InterCaribbean went like this ...... flight changed to 20 min later. We arrive 2 hrs early at EIS to find it's now even 20 min later than that. Head to Trellis for bfast and shopping. Back about an hour before flight to hear we have to rush through security because they're now going 45 min early. Island security made sure that didn't happen but they did end up about 20 min early, from what I could tell, all passengers were checked in so they weren't leaving anyone behind.

Point is their schedules tend to be fluid so check in with them frequently and don't venture too far and too long from the terminal.