OR DO I HAVE TO CONTACT EACH AUTHOR ?

WHICH THESE?
Print then sale, or just print for you?

All fonts have different terms of use.
Just above the "Download" button of each font, there's the license type ("100% Free", "Free for personal use",...)

If it's "100% Free" or "Public domain / GPL / OFL", go for it.
If it's something different and you plan to sell the shirt after printing them, you should contact each author.

I want to print and sell. But I realized ill just use the 100% free ones.