"Flesh and blood" in the more literal sense can mean one of two things. It usually means one's own family or kinsfolk (and is often preceded by "own"). You have to defend or stick by your own flesh and blood, or you never throught your own flesh and blood would behave in such-and-such a way. This probably refers to two traditional concepts: that when man and wife wed they become "of one flesh", and that people related by descent are related "by blood", and the blood of the ancestor runs in the veins of the descendant.

Less commonly it means living body of a human being, as opposed to a ghost or a picture or message or fiction. So a flesh-and-blood person is one you're contrasting with merely a message, memory, telephone call and so on. But you don't normally meet someone "in flesh and blood", you just say "in the flesh" or "in person", because "in flesh and blood" conveys more of the sinews and warmth and beating heart. For example, in the traditional ballad of The Wife of Usher's Well, her three sons are lost at sea, and she utters a terrible wish that they may visit her in earthly flesh and blood:

There lived a wife at Usher's Well, and a wealthy wife was she
She had three stout and stalwart sons and sent them o'er the sea

They had not been a week from her a week but barely ane
When word came tae the carlin wife that her three sons were gane
I wish the wind may never cease, nor fashes in the flood
Till my three sons come hame to me in earthly flesh and blood
Flesh and blood is also a drink. In the Regency novels of Georgette Heyer some of the rougher types, such as coachmen and gatekeepers, have a partiality for it, since it's good and strong and keeps them warm. It's simply gin and port together. Now this sounded rather shocking to me for a long time, not disgusting exactly, but definitely not going together and liable to have quite an edge on it. But one day I happened to have a bottle of each, and lo and behold, it's delicious. Very warming, puts the fire in your blood all right.

The same idea of pale and red drink mixed is found in a modern recipe I found for a cocktail called flesh and blood. (Bloody Mary with gin instead of vodka, in effect.)

1 1/2 oz of gin
3 oz tomato juice
1 dash of lemon juice
dash of Worcestershire sauce
2 drops Tabasco sauce
salt and pepper

Shake very well with ice, serve over crushed ice.