Question: Why does Neil try to convince Charlie that there is no Santa?
Answer: Because Neil thinks Charlie is old enough now that he should no longer believe in fantasy figures like Santa Claus.
Answer: Because some parents don't think it's logical thinking.
Question: When Scott and Charlie are at the North Pole the first time, why did the elf with the pole ignore Scott's talking? Is he deaf?
Answer: The elf on top probably ignored him as he was in no position to answer him. The elves seem to have a stratified society [i.e. some make toys, Judy provides food/beverage, some do security etc.] so it was most likely his job just to punch in the code so the sleigh would descend. With Bernard being the head elf, and probably the most knowledgeable on all things Santa related, he would be in the best position to talk to Scott and answer all of his questions.
Question: When Scott starts slowly turning into Santa, everybody believes he's dressing up as Santa on purpose. Why didn't Scott simply tell people, "I don't think I'm Santa Claus. I'm not pretending to be Santa Claus. I know I'm not Santa Claus. I'm not even trying to look like him." Granted he could never tell anybody how it happened but if he simply said that he isn't pretending to be somebody he's not people might ease up a bit?
Answer: If he told people he was not deliberately trying to look like Santa Claus, that would cause them to be even more suspicious of Scott Calvin having a mental disorder, not a physical one. Remember, Scott went to see his family doctor, Pete, and Pete tried to explain to Scott his physical changes as a matter of changing his diet from milk and cookies, and Scott suffering from a hormone imbalance. Scott tried, but not even Doctor Pete, a professional in the medical field, could help him.
This question is about his mental state. Not his physical transformation. In other words, he could say "There's nothing mentally wrong with me that would make me think for one second I am Santa." His physical transformation could be explained by people thinking he's overeating, growing facial hair and his hair turning white.
Question: Why did Scott visit the young girl's house as Santa Claus twice?
Answer: Why wouldn't Santa Claus visit the same house and the same children each Christmas season? Little Sarah obviously believed in Santa Claus and expects him every year, like many children do. Sarah believed in Santa so much she left him food for the reindeer, and cookies and milk for him, and later, soy milk because she remembered that Santa told her he was watching his fats. Santa will visit each Christmas as often as he can, provided people believe in him.
Chosen answer: Even though Charlie did not want to stay with his Dad for Christmas Eve, he did want to stay at home with a family member, fragmented as it was. Eating Christmas Eve dinner at a Denny's restaurant was not his idea of a Christmas dinner at home with family.