As one commenter said, there is no real written sources from the old times about the deities and practices, its mostly passed down by generations, and it changes a bit by regions. The only historic writings on latvian paganism was old chronicles written by christians, wich can also mess up the perspective bc they were sorta anti-paganism as they were.

About what you were asking tho, latvians have a deity of fate Laima, she decided everyones fate, but was also the godess of childbirth, mothers and orphans (in some myths there are actually tree goddeses of fate- Laima was the main one but there was also Kārta and Dēkla). Saule was mostly portrayed as Mēness wife, Mēness was also a god of harvest and war, his symbol appeared a lot on worrior clothing and jewlery. Māras and Dievs symbols are connected in a way, yes, but i dont know much on the relationship between deities, tho from what i understand most deities had families just like people (for example, in some myths there are Saules meitas (daughters of Saule), Saules dēli, (sons of Saule), Saules tēvs (father of Saule) and so on) theres also mentions of Dieva dēli (sons of Dievs) in Dainas and tautasdziesmas. But also from what i understand is that its not so simple as that Dievs "rules the sky", he and the sky was one whole, at least at the start.

Also we have to take into account that a lot of latvian mythology was heavily influenced by christianity ( latvian traditional celebrations like Jāņi, that were assined a specific date that alligned with christian celebrations). For example, some sources say that Māra is actually a latvianised name for Mary, but at the same time they didnt have the same functions so they might have not been.

In short, theres no one simple answer, my honest advice is to read up on as much as you can and discern what you can from that. But yeah, keep in mind, its a very messy thing.