بسم الله الرحمن الرحيم
(Fatwa: 127/127/SN=02/1437)
In the question mentioned above, your practice (not attending their wedding due to mixed gathering of men and women) is in accordance with Shariah. You should not worry if this practice of yours makes some people angry. But you should not abandon your relatives and should meet them on other occasions. Also tell your parents about the truth why you do not participate in the wedding in order to keep yourself away from these things. Hopefully they would understand it. Also convey Islamic teachings to your brothers, sisters and relatives with wisdom. However, if you hope that in case you participate in the wedding your relatives shall leave those customs in your respect then you must participate in the weddings.
دعي إلى وليمة وثمة لعب أو غناء قعد وأكل لو المنكر فى المنزل فلو على المائدة لا ينبغي أن يقعد، بل يخرج معرضا لقوله تعالى فلا تقعد بعدالذكرى مع القوم الظالمين. وإن علم أولاً باللعب لا يحضر أمثلا …. إلا إذا علم أنهم يتركون ذلك احتراماً له فعليه أن يذهب . (درمختار مع الشامى، 3-501 ط: زكريا)
Allah knows Best!
Darul Ifta,
Darul Uloom Deoband