I want to send in several letters from friends and family to show both sides support our marriage and life together, etc. I don't want to put words in anyone's head, but what should these letters include? Long and detailed or short and sweet? I don't want to annoy CIC with 10-15 very wordy letters of support - or is that what they like to see? And is 10-15 too many?
each of ur family/friends might know something different/special abt ur relationship; maybe with some u went to trips together, with others u would spend holidays/birthdays together, went to their wedding, they came to yours, others would visit u often or u'd visit them, others saw u together go through a harder moment of ur life; all these could show how strong and loving ur relationship is, and u could ask/guide them to write abt it (if they remember)
at the end u need to explain them for what the letter is and to keep it simple and on focus...since u r married and the letters r not mandatory for u, i think 10-15 is too much (they will take long time)...some people send 3-4 and for them they were mandatory (common-law) and it was fine...no matter how many u decide to send, make sure they r from both sides (sponsor and applicant)

also, u could send just a few letters and for the rest of family/close friends reference them in a table (name, contact, relationship, since when they know u); in case CIC needs more, they could contact them...for some members this worked fine too
good luck!