Bad pronouncing nouălea!
Este pronunțat ca al nou - ălea
"eldest" is perfectly good English, especially when referring to humans.
It is, in fact, more common than "oldest" these days ;)
Where does "cel" come from?
Demonstrative pronoun used for the superlative degree of comparison (cel mai)
See https://duome.eu/tips/en/ro section on Degrees of comparison.