The wedding will be outside in the summer. Dress for sun during the day and layers for the evening as the wedding is on the water. Garden party or dressy casual attire for the outdoors. It will be on grass so plan accordingly with footwear.
Yes! The girls are going to be at the wedding and your kiddos are welcome also. There will be kid friendly activities and games to help keep them occupied.
If you are catching the ferry I would aim for the 3:00 or 3:30pm boat, you may need to get there early as there probably will be a line. You can check the ferry website to see how long the ferry wait is ahead of time. You can always make a stop in Langley or there are lots of places to sightsee!