I can understand your anxiety about the kitten, but I don't think you should release the mom cat. You're right to worry about trying to trap her again - it would likely be very difficult.
You didn't mention how long the mom and kitten have been coming to you to be fed. Chances are the kitten is familiar with the location and will return looking for both food and mom. Now that mom cat is in a carrier, try to lure the kitten back by putting the mom out near the trap. Mom will most likely meow, and the kitten, who is probably close by, will hear her. This may bring the kitten out from her hiding place.
I recommend using a kitten trap, since a 5 week-old kitten may be too light to trip the adult cat trap. Use some KMR if the kitten isn't eating any solid food yet; you can also mix the KMR into regular cat food to make it smoother and easier to eat.
Remember to always monitor the trap when it's set. During those times when you won't be around to check it, leave food by the trap for the kitten but don't set the trap. Secure the trap door (with rope or a bungee cord) so it stays open and place the food just inside the trap. You want the kitten to associate food with the trap.
The kitten can survive for awhile without mom, as long as she has a safe place to hide out (which mom cat has no doubt shown her). Of course, eating is very important and I believe the kitten will come back to the food source (you). Eventually, hunger wins out over fear.
BTW, thank you for caring about this mom and her kitten.