I am with Twosleepy.
Esteemed is very formal but the situation seems to be a formal one. Dear is almost always appropriate in writing; in speaking it is less common and carries more connotation of affection than it does in writing.
Less formal (and therefore more common in N. America) would be to say just Good morning/afternoon Ma'am (looking at her,) Sir (looking at him.) In a larger group "Ladies and Gentlemen" instead of Ma'am and Sir.

PS Haven't seen you for a while Callie. Nice to have you back.