Please go through the links here.
It is expacted different place of prayer will be dominated on ethenic line as they are the main service provider and perhaps first to set thing up.
This should not matter as the objective is not to adopt all of their cultural value but to be a good muslims. Islam puts emphasis on community building. For some their ethenic point of reference is one way of achiving this.
1. It is Allah who guides so seek guidance with sincerety and humility. As long as you are part of Ahle Sunnah Wal Jammah (Sunni) - those who follows the due process in seeking knowledge and observation of all aspects of a muslim life, all other lables means nothing.
2. Ismailis are considered by a lot of sunni scholars to be out of fold of islam. So attend the other masjeds. However seeking of knowledge from the salafist should be avoided. You will see they are quiet intolarent and scholasiticly shallow. Most laymen are fooled by them as it penders to ego of ignorance.
In absense of qualfied seassoned scholars, opt for online course. The links are listed here.
3. Do not inform your missguided ex muslim friends. Let your action speaks louder then words. Years of comminsim and miss information will eventually fade when a true example is brought infront of them. Do not argue with the foolish!! When one is humble and sincere and spends time reflecting and studing under a qualafied seassoned scholars, wisdom will reflect in action. So pray/dua for your and their guidance.
Islam is not about inflating ones ego! So keep your heart checked.
I will just tell you one and simple thing spend your time in Allah's Path i.e. spend your time in 4 month find out any masjid near from you talk with them and go in Allah's Path for 4 month if cant make it 4 month dont worry go for 40 days
when you will spend your time in Allah;s Path ( Jamat) you will understand easily Islam Quran Hadith Prophets life, Sahaba's Life Inshaallah it will 100 % beneficial for your self and others also...