in form IMM5406, there is no indication of principal applicant, only the term "applicant", and in the copy that should be completed by your spouse, your spouse's name is placed in the "applicant" and you will be the spouse, and it will be her mother, father, children, brothers, sisters, and her details that will be declared in her form... your form IMM5406 as principal applicant will be placed on top of her form
