Terminology for Teacher Pension Form in Taiwan: "基数“ and ”大口“ Stack Exchange!

I'm currently busy translating an old union pension form for a Retired Taiwanese schoolteacher. 

One of the fillable note sections in the pension lists the number "56" using checking characters (伍拾陆）, followed by the classifier "个基数“ （literally "Cardinal Digit"). 

Next in the note section is this phrase: "领取眷口数一大口。”

My current interpretation is that "Cardinal 56" is a stipulation in the union pension that allows a retired teacher to receive financial support for their single dependent.

Is this interpretation correct? Furthermore, what do the words "基数“ and "大口" usually refer to in Taiwanese financial language?
In the pension form, 基數 means the average monthly salary when he/she applied for retirement. So if the salary was 100 and his/her 個基數 is 56, then the total amount of pension would be 100*56=5600.

For the meaning of 大口, please refer to @thinwa 's interpretation. Just one minor correction, 大口 considers people aged 11 or over.