Im an 18 years old girl,my dress up is not fully Islamic but I don't wear haram or revealing clothes.My parents sometimes suggest me to wear scarf but they don't force me.There are some relatives of mine who often complains about my dress up to me and my mom.I know they tell me because of my own good but sometimes this behavior of them makes me irritated.I just want to know if they have these kinds of rights over me.
Wearing hijab in front of non-mahrams is obligatory. Anyone, not just your relatives, have the right to advise you if you are committing a sin or leaving something obligatory.
That is because the believers are told to enjoin good and forbid wrong (الأمر بالمعروف والنهي عن المنكر). See in the Quran in 3:104, 3:110 3:114, 5:63,5:78-79, 9:71, 9:112, 22:41, 31:17 etc. And also in hadith.