Is this sentence correct?

Yes, the sentence is grammatically correct. You need not use 'who' rather than 'that.' True, you may use 'who' if you wish, but the suggestion that 'that' is incorrect or even less preferred is utterly ridiculous. What's more, 'stewardesses' is a legitimate word. While it is at times considered not politically correct, it is certainly not incorrect grammatically. Thus, rest assured that the sentence you've written is perfectly correct and proper English just exactly as you've written it.

use flight attendants instead of stewardess.

Women who (not 'that').
And, as already stated, say "flight attendants."

Ah yes, the courage to ask what drink you want and point out the barf bag, the daredevils.

yes