Salaams Hazrat.
الجواب وبالله التوفيق
You should care about your friend’s eeman(faith) without a doubt and as a result ask them to directly ask the question, as a Muslim regarding their own eeman from the learned ulamah kiram. After all, tabhleegh is not just asking a question on someone’s behalf regarding their eeman or kufr and then informing them that “they have become a kafir” or “they are still a Muslim”.
It is part and parcel of tabhleegh that through your da‘wah you provoke someone’s feelings to enquire. Ultimately, they should have this much of interest in their own eeman. Do they only have so much interest that they have made you an attorney to ask questions on their behalf? Does the critical issue of eeman and kufr, not motivate them enough to bear the pain of asking a question by themselves?
In the sensitive matters of kufr and eeman, it is the cautious method, for the questioner to ask the question and demand an answer, for both the questioner and responder. The exception to this rule is only if the effect of someone else’s kufr and eeman directly affects someone and they ask the question to rectify their own loss. Based on the situation described in your question, we do not consider it as the exception to this general rule, therefore our original answer still stands.
واللہ اعلم بالصواب