It's very complex but in a basic sense even if they do trade between themselves it is still a massive reduction - losing global trading powers and just dealing with India and China in a limited capacity. Russia also doesn't want to be "reliant" on China, they want to be perceived as equal footing. Their foreign currency is frozen and locked away, the rouble will have next to no value come Monday too. Russia's economy is fecked. Their credit rating is kaput; they can't lend in any reasonable capacity.
India and China are also wary of Russian actions, at the UN Security Council vote the other night instead of voting "No" in step with Russia they abstained, which was genuinely quite surprising.
China is also worried of secondary sanctions and it's state banks are limiting financing for buying Russian materials.