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I would check to make sure that they are not too over watered, or under watered. Both of these could cause defoliation. The soil should be damp but not sopping. If it is dry, you need to increase watering. If it is sloppy, you need to decrease watering and check the drainage holes on the pots.

This could be a watering issue as some ferns need heavy watering.
Certain cultivators are quite invasive and can be difficult to control as you mention. Digging up plants and removing is likely the only way to reduce the invasion into other garden areas.
I would treat the plants with Neem OIl as it may be a fungus issue you are experiencing. Late summer can bring on these issues.

Here are some links for you.

http://extension.uga.edu/publications/detail.html?number=B737
https://www.gardeningknowhow.com/ornamental/foliage/ferns/taking-care-of-outdoor-ferns.htm
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm

It needs more humidity. Either mist it regularly or set it on a pebble tray with water in it to raise the humidity around it. You can remove the brown tips.

This could be from low humidity or they may simply be going dormant a bit early, espeically if you have been experiencing higher than normal temps as much of the country has this summer. They should come back in spring, however.

You will need to move them indoors for winter.

Here is a link with more information.

https://www.gardeningknowhow.com/houseplants/boston-fern/overwintering-boston-ferns.htm

I would recommend that you plan to bring it in before the weather outside becomes unacceptable for it. Starting between now and 2-3 weeks from now for your area will be right. The reason being is that starting the process to bring it in now will make sure that the plant is not as exposed to temperature fluctuations as it might be later on. Rapid temperature fluctuations are harmful to the plant and should be minimized, if at all possible.

To help minimize shedding, you need to acclimate the plant to the indoors. The same as you would need to get a plant use to being outdoors, you need to reverse the process for bringing a plant indoors. This article will help with that:
https://www.gardeningknowhow.com/houseplants/hpgen/acclimate-plants-indoors-winter.htm