There weren't too many baba families in Singapore back in the day. Therefore the chances of the baba families being associated by marriage, alumni or business dealings were quite high.
I understand there were 4 major baba family clans in Singapore before WW2 - the Tans and the Kwas were 2 of them. They control the banks today.
The majority of us whose grandfathers arrived by boat were the poor peasant class.