Attending Hindu festivals

Q: I am a converted Muslim. My parents are Hindu. I face problems from my family's side whenever a festival comes. I want to know that up to what extent I can cooperate with them being a Muslim? On rakshabandhan can I tie rakhi and tilak for my brother?

Stray thoughts

Q: I have a problem, a big problem. Inside my head/heart I always have a whisper that is very wrong if said using my mouth. The whisper is like it is easier if we don't need to do ghusl like others, whisper like ghusl is a burden. It happens in my head. Afterwards, I quickly do istighfar and say Lailaha ilallah muhammadur Rasulullah. I am afraid. I know its very wrong if I said that with my mouth and can be kufr.