Is the father sinful for not inquiring about his two daughters whose mother died after their birth, and who were taken care of by their maternal uncle, given that the father was unable to care for them due to his financial circumstances, and what is the expiation for that, if any?

The father was obligated to care for his daughters and provide for them. If he was unable to provide financially, he should not abandon their care and visiting them, for that is part of maintaining kinship ties and strengthens love, and abandoning that leads to estrangement. Inability to provide financially does not justify abandoning the rest of his responsibility. The questioner is advised to consult the Sharia (definition) courts regarding the inheritance if the father left behind any wealth.