The photographer should strive to take close-up shots of the butterflies landing on people, rather than photos of them flying away. Also, you can put a few butterflies in a refrigerator for 20 minutes, then place them on a bouquet or wedding gown, etc. Butterflies cannot fly in the cold or the rain. You will not be able to release them outside, and instead will have to postpone the release until later that day, or the next day. You can place the packaged butterflies in your refrigerator for a day or two to keep them safe and comfortable while waiting for the weather to clear up.
Some people do have indoor releases in well-lit facilities.
These types of release are fraught with danger for the butterflies, because they can easily be stepped on, and they become disoriented indoors. They will head for overhead lights and windows, and may injure their wings in attempting to escape. A better alternative is to make a simple, temporary display cage from bridal veiling wrapped around a wood or PVC frame, a birdcage, a wrought-iron stool or table, etc. Place the frame on top of a large piece of bridal veiling, add a bouquet of flowers, and draw the veiling up to the top, trying not to create folds where the butterflies can get trapped. Slip the butterflies inside, then tie a ribbon and bow around the gathered veiling at the top of the cage.