Sorry to hear this has happened. I know from watching friends and family members who have gone through this that it is very difficult for all involved.
THC by itself may have caused this. It is responsible for more trips to the psych ward than any other drug by a wide margin. THC gummies are notorious for improper labeling. We don't know if he was having the equivalent of a "beer after work" or if he was on a major bender. Him being in his early-to-mid 20s with a history of drug use (family history of mental illness?) makes him a statistic when it comes to schizophrenia diagnoses.
The less bad news is that it sounds from your post like your brother's experimentation with his serotonin status pushed him over the edge. This means he can likely recover fully given a proper recovery protocol. To any Bulgarians-in-waiting, you need to be a Level 5 Peater before your stack gets that big.
Practically speaking, has your brother been diagnosed as schizophrenic or with anything in particular? This impacts what public or hospital resources might be available to you/him. Healthcare "practitioners" can't help you through the bureaucracy. If a social worker is involved, he or she is a great person to ask about what you can do as a family. I mention this because the emotional strain on family relationships is severe in cases like this and because your brother will one day soon be off of whatever wild meds they have him on now and coming off of those is hard. The trick right now may be to find him treatment/ a place to stay until he can get medical assistance, since he has no income.