Article 185 was evidently only applied to the heir closest to the throne, the Heir-Tsesarevich.
The inspiration/basis for this limited interpretation might be interpreted as coming from Article 35, which deals with the religious requirement should the Throne, upon the extinction of the agnatic line, pass via the cognatic line to another reigning house:
Когда наследство дойдет до такого поколения женского, которое царствует уже на другом Престоле, тогда наследующему лицу предоставляется избрать веру и Престол, и отрешись вместе с Наследником от другой веры и Престола, если таковой Престол связан с законом; когда же отрицания от веры не будет, то наследует то лице, которое за сим ближе по порядку. Там же.
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When the succession reaches a female branch which is already reigning on another throne, it is left to the person who succeeds to make a choice of faith and throne and, together with that person's heir, to renounce the other faith and throne, if such a throne is tied with a religious denomination; if there is no renunciation of faith, the succession passes to the person next in order.
There is no explicit demand for other members of the IF to profess Orthodoxy or ban against baptism or conversion into another faith, so in theory it was possible, although it would have caused a major scandal and probably would have led to the Emperor issuing an autocratic manifesto or ukase stripping them of membership of the IF, considering that the whole point of the IF was to provide heirs to Throne, whose occupant had to be Orthodox. There was of course also an issue with the oaths of loyalty male members of the IF had to swear to the Emperor, I don't know if they demanded the oath-taker to be Orthodox.
