My brother is the most unhygienic person I know

Title is pretty self explanatory and gets the gist of it but my brother is the most unhygienic person I know, or can think of. He rarely showers, brushes his teeth, washes his face or even goes outside/ opens a window. His room smells disgusting and he pretty much sits in it all day too. He’s 15, and I know it’s normal for teenage boys to struggle with self care as they hit puberty but it’s getting to a point where it’s unbearable. My mother, father, uncles, aunts, hell even my grandmother and I have all done our best to talk to him and get him to take more care of himself but it’s all to no avail. I have offered to take him to stores to get hygiene products that he enjoys when I have days off work but even that doesn’t get anywhere, he will literally sit and stare at products before using them. I don’t know what else to get it through his head that he needs to be clean. Any and all advice and offers are appreciated.