Regarding the deity Agni, there are multiple mythological references to his origins. In some texts, Agni is described as being born directly from Lord Brahma, while in others, he is said to be the son of Sage Angiras or the offspring of various gods and goddesses. Agni is often considered a divine entity in his own right, associated with fire, sacrifice, and transformation.
Sage Marichi is indeed often considered one of the mind-born sons (Manasputras) of Lord Brahma, and Sage Angiras is considered one of the great sages (Rishis) in Sanathana Dharma.
As for the deities Sun God (Surya) and Agni, they are both revered and ancient deities in Proto Indo Aryan narratives and not just in Vedas. Their origins and relationships can be interpreted differently in different texts. While some texts may present Sun God as being older or more primordial, others may assign different lineages or connections to these deities.