1- Pray for his hedayah daily. Don’t give up. Sometimes after many years Allah guides a person
2- Let him write Sura Falaq and Naas and wear it an armband when trying to pray. This could be effective. Wearing the Herz of Imam Jawad (a) is also recommended. Even if he feels sick, let him pray for a few days and hopefully the feeling of sickness will go away and decrease
3- Be creative and find effective ways to convince him to pray.
Please see this video and use some of these points to attract him to prayer:
4- Pray Salat Ja’far al-Tayyar and ask Allah to guide him
5- Recite this Du’a