If your budgies have overgrown nails, there is something wrong - either you are feeding way too much protein and/or the perches are not good (never use dowels, always use natural tree branches with the bark on them and of different diameters). But, to start them off comfortable even as you change the diet and/or perches, you can do it yourself very easily. Towel each of them (use a kitchen towel, not a real towel even if it's a hand one because they are too thick and would not give you enough of a 'feel' so you might squeeze too hard) and putting them belly up on your lap, grab each foot and separating the toes (the bird will clench the foot into a 'fist') trim the nails (watch out for the quick so don't do too much) the same way you would do a dog or a cat. I use a nail cuticle clipper like this one:
https://www.amazon.com/Swords-Germany-m ... 63&sr=8-17The natural branches will trim the excess naturally but, if you want to speed up the process, you can always use sweetfeet perches for their roosting ones (the ones that go all the way up on the cage which are the ones they use for sleeping). These are the sweetfeet:
https://www.amazon.com/Sweet-Feet-Beak- ... 754&sr=8-1They have a smooth side for the bird to rest their feet on and rough sides for the nails to be kept trim. They are inexpensive, very easy to wash and they are not even and round (which is very bad for their feet because they atrophy the muscles of the feet and legs and give them bumblefoot).