Can my guests upload videos from their phones or do they need to use your record feature?

Yes, they can upload by tapping the "upload from library” button, then tap the target.

This is great for uploading videos they may have recorded during the ceremony, or perhaps, during the speeches, first dance, father/daughter dance, mother/son dance, and anything else you'd like to preserve.

In fact, it's a good idea to arrange with someone in your bridal party beforehand to capture a few of these special moments and upload them later.