He was bequached yin power as well if you look at it Hashirama also has Yin release. So does Naruto after power up. Yet Sasuke has only Yin release So it's likely and obviously stated in the manga that Indra had the yin chakra of the sage. Which also confirms you only need yin release for Rinnegan(potent enough and Ashira is a non issue).
Hashirama does not have yin release. Bringer of darkness is just a jutsu, which anyone in the series is able to use one form of base genjutsu even Naruto.
You're confusing 3 types uses of yin and or yang. Which is element, energy, and kkg.
1. there is yin element and there is yang element that are all in the basis of ninjutsu. This is upon to any shinobi to use depending on your level of manipulating the properties. Part 1 naruto feats that Kakashi was doing since the Zabuza arc.
2. Yin energy and Yang energy. Yin energy is mental energy that works the spirit while yang energy is physical energy that works the life force. Uchihas have great mental energy in their optic nerves chakra while the Senjus have great physical energy in their bodily chakra
3. Yin seal=Six path shadow and Yang seal=Six path light. This is the power Hagoromoo is able to bequeath to people that summon him. In each of these hand seals carry great power to defeat a God. Momoshiki bequeath Boruto a seal in his hand after he defeated him which is yet to be expanded upon in its potential. Naruto and Sasuke showed their own seal potential on madara for a short while before Hagormoo taking them back. Ashura unlike naruto and sasuke had both in each hand, and use that to combat his brother Indra to the death.