1901 and 1903, that early? You ggf must be over in Canada before your gf and his siblings came over. The custom then was for members of the older generation to advance the head tax money and the younger generation will repay it or worked it off.
To find the village head honcho all you have to do is ask a village inhabitant. It is similar to being the mayor. I read they even held elections for the position and recently non-party members are being elected.
The clan head honcho is generally the eldest male. If you give the villagers your father/grandfather/granduncle's names they may be able to direct you to the ancestral home if it still standing. Then the next step is to meet the head honcho. As a visitor from "Gold Mountain" the visit to the ancestral graves would be more elaborate in terms of offerings and the subsequent gathering. In the smaller villages all inhabitants of the village were invited.
By married name I guess you mean "hao". This may or may not help. It all depends on the communication between your grandfather and the village. If they were married away from the village and with no communication, the village may not know their "hao". But since you said the fourth brother went back then the chance is good they'll know their "hoa" and may be even your father and his cousin's names.
In order for my cousin to give it a shot we'll need everybody's Chinese names. I think we can start with the village name on the certificate you emailed me. Have you have a chance to check your grandfather or father's tombstones? There should be their Chinese names and the name of the village.