Satguru / Guru is used for God, Shabad Guru and Sikh Gurus. However it does not mean that Gurus when referring to Satguru or Guru were praising themselves, context matters. God is Primal Guru as Satguru / Guru is one of his name, he removes the darkness and without his wish you can't get mukti. Those who believe in him are Gurmukhs, both sikhs and non-sikhs. Devotees like Prahlad and Dhruv or Bhagats like Kabir, Farid, Trilochan etc are not sikhs. Gurbani believes anyone can get mukti as long as you believe in Naam Simran of God. I already answered then why be a Sikh in query 8. Yes Gurus are referred as God in some shabads but we don't worship their physical body because they themselves told to worship only Formless God which they were part of and we all are. Sikhi focuses on ੴ. Anyone saying only Sikh Gurus can give you mukti or only Sikhs and Khalsa are getting muktiis trying to get ownership of 'right way' or God which is against Sikh principles.