Impaired are: tyrosine to dopamine, tryptophan to niacin, cystathionine to cysteine. Which cofactor and vitamin is common to all three pathways? Ty

Not an easy answer. These pathways can be impaired due to a primary disorder or secondary to other conditions interfering with metabolic pathways. Until a thorough investigation has been done, it is not likely that you will find a simple solution or single co-factor that will treat your biochemical imbalances.