Hotel
Reach out to them and mention "VanRoosendaal wedding."
Train
The Peter Pan bus is the best public transport option from Boston down to Falmouth. It departs from South Station (both Amtrak, and other bus companies travel in there), and you want to book the "Falmouth bus Depot", which is the second to last stop. The last stop, Woods Hole, is also only a few miles away, so not a huge deal if you miss it.
Hotel
Here are some other hotel options in the area. We recommend staying in Falmouth for ease of access, as traffic can be brutal in the summer time.