Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with a doctor.
Without the ability to examine and obtain a history of your father, I can not tell you what the exact cause of the symptoms is. However I will try to provide you with some useful information.
Emotional and/or behavioral changes following a stroke is common. Depression may be seen in up to 20% of post stroke patients with another 20% meeting minor criteria for depression. It is difficult to say how long each patient will be affected by the psychological changes. It has been estimated that depression may last 9 months to 1 year if left untreated. The treatment options include SSRIs, TCAs, and possibly low doses of stimulants. (These agents will need to be used cautiously if blood pressure or cardiac risk factors are present).
Additionally, behavioral changes can occur as a result of the structural lesion/location caused by the stroke.
I would suggest that your father be seen by a psychiatrist or a stroke neurologist. He may need medication to help him through this phase of recovery.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.