If they have faith in Christ they could not remain in the Catholic Church; I could not remain in the Catholic Church. Christianity and the faith of the RCC are at polar opposites of each other.I don't think they have denied any of this; I think they simply have a misunderstanding. If they have faith in Christ, they are saved -- period.
Can a person be a Muslim and a Christian at the same time?
Neither can a person be a Catholic and a Christian at the same time.