What is the function of 而 and 為咗 in 我哋為咗決定去邊度度蜜月而閙交 in Cantonese?
[為咗 A 而 B] = [ to B for A]. It is a two parts function word for  "for "

[(為咗) cause (而) verb]  =  [verb (for) cause] 

Example :

"(為咗)钱(而)工作" =  "work (for) money" 


  [我哋(為咗)決定去邊度度蜜月(而)閙交] =  [we (to) quarrel (for) deciding where to go to have honeymoon] 


In English, we have to omit "to" before the verb if there's a subject in the sentence , e.g. "to work for money" -->  "I work for money". but we don't omit "而" in "我為咗钱而工作" in Chinese, because [為咗 cause 而 verb] is a set structure.