Is it permissible for a father suffering from bipolar disorder to be the guardian (wali) in his daughters’ marriages, or should his brother undertake that?

Bipolar disorder is not considered insanity, but it affects the patient with episodes of depression or mania. The guardianship of a father afflicted with this disorder is valid if he is sane, aware, and capable of evaluating suitors. However, if the illness prevents him from researching or evaluating suitors, the guardianship transfers to the next closest guardian, such as the grandfather or brother, because a person whose judgment is impaired by old age or mental instability has no guardianship due to their inability to investigate the circumstances of prospective spouses.