What should I do regarding my father's request that I take out a loan for him, given his refusal to attend my wedding and his status as my legal guardian for the marriage contract if I don't, and am I religiously obligated to obey him in this matter?

Obeying a father is not obligatory if he requests an interest-bearing loan. Nor is it obligatory to obey him in taking a permissible loan if it causes hardship to the son, for a father is not permitted to take from his son's money that which harms him or causes him hardship. If the father refuses to marry off his daughter because of her rejection of taking a loan, an attempt can be made to convince him through relatives, friends, or the Imam of the mosque. If that does not work, the matter should be referred to the Sharia judge to compel him to marry her off. If he refuses, his guardianship lapses and transfers to the next guardian in line.