Is one sinful for attending a mixed-gender wedding out of a desire to maintain kinship ties?

If one is invited to a banquet where there is an evil, and he knows about it before going and is capable of changing it, he should attend and change it. If he knows about it and knows he is unable to change it, it is forbidden for him to attend. If he attends without knowing, then learns of the evil, he is obligated to denounce it; if the evil ceases, he may remain, otherwise, he should depart. If he knows of an evil present but neither sees nor hears it, he has the choice to remain or to depart.