my devices are unable to stay connected to wifi via airport/time capsule

A 3rd Gen Time Capsule would indicate that your product is at least 4 years old and depending on when you bought it, as much as almost 6.

Based on a number of years of forum experience with these products, including the model that you have, the useful life....on average.....of the earlier generation Time Capsules is about 3 years.

One of the symptoms of a Time Capsule power supply which is starting to head downhill is that the wireless radio will start to have intermittent drops, which will continue to occur more and more frequently.

At this point, as a kind of last gasp measure, I would recommend that you reset the Time Capsule back to factory default settings and then set it up again. You won't lose any of the data on the hard drive if you do this, and you can use the same wireless name and passwords that you used before if you wish.

If you continue to see wireless service drops after you do this, the evidence is pretty clear that you will need to replace the Time Capsule as your wireless router. When you do this, you can keep the Time Capsule on the network, turn off the wireless, and simply use the Time Capsule as a wired hard drive until it fails.