I have a question about nuseri.One of my cousin is nuseri so can I go to his house and sit with him and even eat with him? What are qol e masoomeen? My family members are telling me to bycott them due to their ghulat extremist beliefs such as Imam Ali is Allah Astagfurallah.

It is a trial time for everyone. According to tradition of Ahlul bait as Aakhir zaman is challenging time for believers to protect themselves from influence of wrong beliefs.
May Allah guide us and keep us on right path if someone remain on path of ahlul bait as according to Hadith of imam Mohammad Baqir as he will get reward of 1000 martyrs of Badr and Uhad.
Yes it is challenging your father is absolutely right and my sincere respect for him and my elders.
But today we are divided and momeneen are labeled as Muqassir or two ghalat two extreme end According to Rasul saw and Imam Ali as both are wrong and in astray
But many of us are not properly guided but misguided in planned way. Why not we guide them in proper way in quranic way

Holy Quran 16:125
ادْعُ إِلَىٰ سَبِيلِ رَبِّكَ بِالْحِكْمَةِ وَالْمَوْعِظَةِ الْحَسَنَةِ ۖ وَجَادِلْهُم بِالَّتِي هِيَ أَحْسَنُ ۚ إِنَّ رَبَّكَ هُوَ أَعْلَمُ بِمَن ضَلَّ عَن سَبِيلِهِ ۖ وَهُوَ أَعْلَمُ بِالْمُهْتَدِينَ

Invite to the way of your Lord with wisdom and good instruction, and argue with them in a way that is best. Indeed, your Lord is most knowing of who has strayed from His way, and He is most knowing of who is [rightly] guided.

I think help them guide them they need proper guidance and do not give chance or an opportunity to enemies of Ahlulbait as. I’m sure your effort shall not be wasted.