Should I attend the same-sex or transgender wedding of a family member?
Your question indicates the tension you already see and feel – a grief of heart over the present situation and consciousness of the cost about the decision you face. My heart breaks over the painful path down which you must go, but I will rejoice if you walk it faithfully.
In such situations, the love of affinity and proximity (family and friends) must give way to the love of supremacy and priority (the Saviour): in other words, God must come above every earthly tie.
You will need to remember the teaching, the warning, the comforting, which goes with that commitment, for our Lord told us that he must come first, that following him will divide us from our earthly nearest and dearest, and that he will not leave us destitute (Luke 8:19-21; 12:52-53; 14:26).