Well first of all they had offices in "all over Somalia" is incorrect they had offices in Italian Somalia and British Somaliland is the correct expression or you can say the Somali Republic, cause at that time Somalia only was the south. Even today the correct name must be the Somali republic. Somalia and Somaliland as well are our colonial names.Wasn't Egal AUN part of the party? The SYL was by far the most popular one all over, they had offices all over Somalia proper and in Djibouti, Jigjiga, Harar, and NFD. It didn't represent any one group only.
Cigal AUN was as Fidmeer said not part of SYL at that time, they had a very little presence in Somaliland. The negotiations started around the year 1957 and the three parties from the Somaliland side were SNL the biggest party and the party of Cigal, NUF the second biggest party and the very small party (within Somaliland small) SYL. According to the Marxum they started the talks in 1957, because they wanted to unite the five Somalis and Somalia was the only partner to negotiate with.
Cigal AUN was against the union from the very beginning, but you have to understand that both parties SNL and NUF were "Isaaq dominated" parties, hence they accused him of blocking the union so that he can become the head of the state of Somaliland (Isaaq hate it when other Isaaq rule them). All the mentioned events can be seen in his speech in Youtube, he is a brilliant speaker look it up if you are interested.