The plural possessive is "ladies'." "Lady" is singular, so if you were referring solely to one woman's shoes, it would be "the lady's shoes." As for your second question, I'm assuming you're referring to a group of women in your salutation of them, so it would be "Good morning, ladies." And as you're addressing them directly, the comma preceding "ladies" is necessary. Hence, there is no ambiguity with the men, and for the same reason no ambiguity with the ladies. Ladies is the plural form of lady, so the apostrophe goes to the right - ladies'.

Understanding the Context

If you are wondering why we don't write ladies's, it is because ladies is one of the exceptions, along with girls', parents', players', weeks' and even Klingons' Ladies Captain means the Captain responsible for Ladies Golf elected to represent the Lady Members at Club and County level and to fulfil [sic] any requirements of the relevant Golf Association. The metrical pattern of "ladies and gentlemen" consists of (arguably) two dactyls. A dactyl is a group of three syllables where the first is stressed and the second two are unstressed. Both "Ladies' Beer" and "Ladies Beer" are acceptable, but there is a slightly different implication depending on which you use.

Key Insights

"Ladies' Beer" is written in the possessive form, and thus implies ownership. Should "Ladies" be marked with an apostrophe in the noun phrase "Ladies ... 10 Apart from guys, which is fine and the most obvious choice, as others have mentioned, you could use ladies, which has a tinge of both irony and flattery. Most women appreciate this. Ladies is best accompanied by slightly exaggerated punctilio if the speaker is a man.

Final Thoughts

I've been wondering. Where did the saying "Ladies first" originate? Did it originally appeared in English countries, or? And is this always expressed in a positive/polite tune of meaning? I mean, ...