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It has a pest that is creating this. They are likely scale and hard to see. This article will help:
https://www.gardeningknowhow.com/plant-problems/pests/scale-bug-how-to-control-plant-scale.htm

While Boston ferns typically prefer to be kept a little pot bound, if it is getting difficult to water, especially if the water doesn't seem to be penetrating the soil well, or if you see roots coming from the pot, then it is probably a good time for repotting. In this case, you would go up a couple inches in diameter or two pot sizes, even if it's in a coconut liner go up in size. However, if your plant looks healthy otherwise and doesn't seem to be having any issues, then simply let it be, though you can add in some more soil if necessary.

Here is an article that you may find helpful: https://www.gardeningknowhow.com/houseplants/hpgen/learn-more-about-repotting-houseplants.htm

As long as you are just poking the baby's breath stems into the soil in between the leaves, it should not cause any issues. If the Boston ferns will be moving from an indoor location (home) to an outdoor location (wedding) or vice versa, you will want to limit how long they are in the new location. The longer they will be in an opposite location to what they are use to, the more stress they will experience - which could lead to problems. It is not as much of a concern if they are say indoor ferns and this is an indoor wedding. I just thought I would let you know in case.

Your fern may have some environmental issues cause this.

To much light, heat, watering issues--to much or to little.
Wind can be harmful to your fern also.
A cool location with some filtered light, away from wind. Water daily and even twice a day if the temperatures are above 85 degrees.

You can clean up the dead and damaged leaves.
Watch for insects or disease as a stressed plant can invite these things.

Here is a link that has more information.
https://www.gardeningknowhow.com/houseplants/boston-fern/boston-fern-care.htm

The following article will help with fertilizing these plants: https://www.gardeningknowhow.com/houseplants/boston-fern/boston-fern-fertilizer.htm

You can always prune out the unsightly looking fronds and they should regrow just fine. This article will help: https://www.gardeningknowhow.com/houseplants/boston-fern/trimming-boston-ferns.htm

This article should help: https://www.gardeningknowhow.com/houseplants/boston-fern/boston-fern-fertilizer.htm