How do I decide if nails need to be clipped? IS it possible that cockatiels don't have problems with overgrown nails? (I know that special "filing down" perches help with this)
I never thought we had a problem but now I think some nails are getting too sharp and long

You will know if they are too long because they will start to Kurl.The nail should be nice and short.If they are sharp you just file them down.

I had to say C url like that because you cant say it or else it doesn't let u post.

When they feel sharp

I saw this drawings in another forum, thought it may help

when a bird is on my shoulder and I am wearing something thin. Or, when I pick the bird up and hold in my hands, and the nails feel sharp to my skin

I am thinking how much it would be to clip nails for 10 birds...

Human discomfort doesn't necessarily mean that there's a safety issue for the bird. But you have to watch the length, as others have said. Another sign that nails need clipping is if the nails are getting caught when the bird is standing on cloth, because this can lead to foot injuries when the bird tries to get loose or tries to fly away.

You can clip the nails yourself. It isn't that hard. All you need is to just cut the tips off. You might need a second person to hold the bird but it gets easier with practice. I can cut my bird's nails myself.

multiple by 10

I have never clipped my tiels' nails.