Is it permissible for a committed and niqab-wearing fiancée, who has traveled to stay with her bedridden grandfather and grandmother in another province, to mix with non-mahram guests who spend the night in the same apartment and share facilities with them, and to serve them food and speak to them, even if she wears a niqab, especially given the fear of her being exposed to a stranger or corruption creeping in?

A woman's travel without a mahram (definition) is not permissible except in cases of necessity and urgent need, such as the illness of a grandmother, provided there is safe company and adherence to Sharia (definition) regulations.

As for a woman cohabiting with non-mahram men in a single dwelling with shared facilities, such as the kitchen and bathroom, or serving them food and conversing with them, this is not permissible according to Sharia, even if a mahram is among them, because it is a likely cause for unlawful seclusion (khalwa (definition)).

It must be noted that a suitor is a non-mahram to his fiancée before the marriage contract, so he is not permitted to speak with her except out of necessity.