Is it permissible for an illegitimate child to communicate with his biological father and his siblings from him, and is it permissible for him to conceal the secret of his birth from his maternal siblings, and who inherits from him, and has he committed a prohibited act against his siblings in the same house?

A child born out of wedlock is legally attributed to his mother, not to the fornicator, and neither inherits from the other. This is the view of the majority of jurists. If there is an embarrassment in attributing a child born out of wedlock to his mother, he should be attributed to a general name such as "Ibn Abdullah." Adoption is forbidden in Islam, so it is not permissible to attribute the child to the one who adopted him, and no inheritance or filial rulings result from it. A child born out of wedlock is not obliged to inform anyone of the truth of his lineage, and it is better for him to conceal himself and his mother. He must be careful not to be alone with the wives of the man he lives with — other than his mother — and his daughters from other than his mother, as they are not his mahrams.