Does my ownership of a room in my grandfather's house, despite not living there and having my belongings in it, count as an injustice to the other heirs? And what is required of me to do?

The room is owned by the heirs, and their silence regarding its utilization may signify their consent for your continued stay, based on the jurisprudential maxim: "Silence in the context of need is an articulation." However, if you know that they are refraining [from asking you to leave] out of shyness towards you, or if they wish for you to vacate, then you must vacate it for them. This is because what is taken by the 'sword of shyness' is not permissible, as it is akin to coercion. Furthermore, consuming a gift presented in this manner has been prohibited.