Sarita and Miya both already use WhatsApp. Both felt comfortable using it for this group. Ev installed it immediately. People were playful with it immediately, sharing and having fun with it.
The day after, Miya posted a video summary of her conversation with May!
The following week, I asked May and Heather if they used WhatsApp, and if so, whether they wanted to join the group. They both said yes, and they both have posted since.