The Hashiras would likely show concern. Some, like Shinobu, would immediately start looking into possible medical solutions. Giyuu might be more reserved in his worry but would still keep a close eye on Tanjiro. The other demon slayers would also be affected. They look up to Tanjiro, so his sickness would lower the morale of the group. They would try to support each other while waiting for Tanjiro to recover.
He might be angry at first. Naruto has grown up alone and had to fight for acceptance. So when his parents say they regret abandoning him, he could lash out, saying it's too late. After all, he has already faced so much without them.
The son could ask for some time and space if he feels too overwhelmed in the moment. Then, when he's ready, he can sit down with his parents and have a proper conversation. He can also share some educational resources about homosexuality with his parents to help them understand better.
In some fanfictions, Naruto may become extremely bitter. He could feel a deep sense of betrayal and this might fuel his determination to become stronger, not for the sake of the village at first, but more for self - vindication. He might isolate himself from others and struggle with his identity.
In some versions of the fanfic, Harry might have a sort of instinctive understanding that his parents had a good reason for leaving him there. So, while he's still not happy about it, he might be a bit more accepting. Maybe he can sense some sort of protection spell around the Dursleys' house that gives him a small sense of security.
Tanjiro might use his sense of smell to detect hidden threats. Since his sense of smell is super - enhanced, he could sniff out any demons or traps in the way of saving Rengoku. For example, if there are demons disguised as allies, Tanjiro would be able to tell by their scent.
I recommend "The Peasant Daughter-in-law". The female protagonist of this book also raised a child alone, while the male protagonist was the eldest young master of a peasant family. The plot also involved the situation where the female lead avoided certain people in order to protect her child. The entire novel was set in business and farming, telling the story of how the female protagonist started her own career and found true love. I hope you like my recommendation, Mwah~