Q. 1. Are Protestant Baptisms valid?
A. 1. As a general rule, Protestant Baptisms are valid.
Q. 2. why are they valid?
A. 2. They are valid because they usually meet the three Catholic Church requirements of proper matter, form and intention. That means:
a. Proper matter means tue and natural water was used.
b. Proper form means the minister poured, completely immersed in water, or sprinkle water upon the candidate, while saying the words, “I baptize you in the name of the Father, and of the Son and of the Holy Spirit.”
c. Proper intention means the minister of baptism had the intent to baptize as the Church intends.
If there is doubt as to the validity of the Baptism, the person in question is baptized conditionally. That does not mean that they are being baptized twice, since such is not permitted under Canon Law. It means that if the person was not properly baptized, then the conditional baptism is valid. If that person was properly baptized, than the conditional baptism is not valid.
What determines if the baptism is valid or not in a conditional baptism is the "intent" of the person administering the baptism.