Love overcome all obstacles in life...if that person really love you then that peron will do what ever it takes to be with you...hence "by all means necessary". It will be entirely up to that person, in the mean time prepare your self just in case the relationship goes south...then move on with your life and be happy with the outcome because things happen for a reason.
You can find other times and places to be with that person. You don't need to throw this into their family's face and barge your way into the gathering. Maybe over time, they'll get past their objection and allow you into their family activity. Until then - lay low,