Can a person with many sins who suffers from epilepsy and schizophrenia be among those brought near in Paradise if he asks Allah for that, and will his suffering intercede for him, or is his asking considered an transgression in supplication and an act of despair?

We ask Allah to grant you healing, for Allah has made a cure for every disease. This includes ruqyah, adhkar, and du'a with certainty. Sins are a cause for every tribulation in this world and the hereafter, as mentioned in the Quran. Therefore, you must hasten to sincere repentance and cease committing sins. Illness can be a means of expiating sins, but one should not be deluded by this, because sins destroy their perpetrator if they accumulate. Asking Allah for Paradise while having sins is not an aggression in supplication, but repentance is obligatory, and do not despair of Allah's mercy.