Are angels heirs of God?

No. "Christians are joint heirs with Jesus Christ through redemption (Romans 8:17) which is made theirs by faith in Him based on His death at Calvary. Angels are not joint heirs and must stand aside when the believers are introduced to their boundless, eternal riches. The holy angels, however are ministering spirits have never lost their original glory and spiritual relationship with God. This assures them of their exalted place in the royal order of God's creation" (Billy Graham, Angel's God's Secret Agents, pp. 41-42).