C&C Generals Zero Hour Online play

My father and I bought the C&C Ultimate Collection on two different PCs and on two different Origin accounts. The only thing the two accounts have in common is that the two C&C games were bought with the same credit card. Whenever I tried to create a game in multiplayer so we could play a game against each other, my father logged in to his generals game and went into multiplayer and when he signed in, the game signed me off. Then when I tried to log back on it logged him out. I am confused as to why this happens since its two different accounts for both Origin and Generals.