All the people who receive the invitation to add their messages will be able to do so without restrictions. There is no limit of collaborators, so unlimited messages can be added to the group card.
Along with the text messages you can add images or animated GIFs that will surely make them smile or remind them of the magnificent moments you have spent together.
If you prefer, you can also record a personal video with your message of support and add it to the group card. In most cases, a video is a much closer message with which you will surely be able to gladden the recipient.
You can choose the ideal template for your group card among multiple templates that you will have available in your client area.