Which civilizations have the Half-Brothers card?

Germans, Swedes, Maltese and Poles.

What does Half-Brothers do in AoE3?

Turns Carolean into Order Musketeer; Turns Sentinel into Order Musketeer; Ships 0.5 Order Crossbowman per Strelet; Ships 0.5 Order Musketeer per Rekrut. The game says: "Replaces your Heavy Ranged Infantry and Rifle Infantry with Order Musketeers and Order Crossbowmen. These units have increased hitpoints and heal automatically."

Home City card

Half-Brothers

Half-Brothers (tech ID DEHCREVHalfBrothers) is a Home City card in AoE3: Definitive Edition 100.19.18309, in the decks of 4 civilizations, sent from the Industrial Age. Effect: Turns Carolean into Order Musketeer; Turns Sentinel into Order Musketeer; Ships 0.5 Order Crossbowman per Strelet; Ships 0.5 Order Musketeer per Rekrut.

Quick answers (3)

Which civilizations have the Half-Brothers card?: Germans, Swedes, Maltese and Poles.
What does Half-Brothers do in AoE3?: Turns Carolean into Order Musketeer; Turns Sentinel into Order Musketeer; Ships 0.5 Order Crossbowman per Strelet; Ships 0.5 Order Musketeer per Rekrut. The game says: "Replaces your Heavy Ranged Infantry and Rifle Infantry with Order Musketeers and Order Crossbowmen. These units have increased hitpoints and heal automatically."
What is the tech ID of Half-Brothers?: DEHCREVHalfBrothers.

Replaces your Heavy Ranged Infantry and Rifle Infantry with Order Musketeers and Order Crossbowmen. These units have increased hitpoints and heal automatically.