Are we sinful if we agree to a new suitor after the father delayed responding to a previous suitor residing in Saudi Arabia, knowing that the latter has arranged his affairs to come to Egypt soon, and rejecting him might hinder him?

If a woman does not approve of the first suitor, there is no harm in entertaining another suitor, because the engagement that is forbidden upon another engagement occurs when the woman has accepted the first suitor. The proof for this is the hadith (definition) of Fatimah bint Qais, may Allah be pleased with her, when Mu'awiyah and Abu Jahm proposed to her. The Prophet, peace and blessings be upon him, then proposed to her for Usamah ibn Zayd, because she had not yet accepted either of them. It is recommended to inform the first suitor of the rejection if the second one is accepted.