Does knowing multiple hash of the same content make it more likely to generate original plain text? Say I'm trying to brute force the original plain text of an SHA256 hash, does knowing the RIPEMD160 hash of the same text help? In other words, does providing access to hash values of the same text generated by multiple algorithms decrease security?
No, there is no security decrease in this case. While there could be some hypothetical constructions that might leak the preimage if two images are known, this is definitely not the case for existing hash functions, which are all quite different from each other.

An example of such a weak pair of hash functions could be two versions of MD5: one with 63 rounds, and another one with 64 rounds. Then the two hashes would reveal partial information about the preimage.