This depends on the intention of the person that did the vow â€“ nathir. If he meant especially writing on paper, then it becomes obligatory to do so. If he meant composing in general, then this could be done by writing on paper or by presenting the information of the book in any form.
If the marja who you emulate has an actual edict on the issue related to marriage – or any other issue – then one must act in accordance to his edict and he is not permitted to refer to another marja. If the opinion of your marja is compulsory precaution on a particular ruling, then it is permissible to refer to the opinion of another marja.