Ok so coming from a bed wetter, your child may or may not out grow it. I know for me it was muscle (yes they can do surgery after age 18 to correct or sooner if needed)
or mental (no not crazy, but psychological and can be so hard for a kiddo or adolescent. I would say have him seen and make sure he is ok about it all and it's not inhibiting (enabling) him from progress. Also mental is was he ever abused? I was for over 8 yrs by a family member and no one knew, and it can haunt them for life.)
Now how to deal, use amonia to celan up with with lemon helps or a good stong cleaner like lysol but be careful of clothes and fabric can discolor. Make sure he cleans well.
After 7 pm fluid yes that is great it will help a lot if it's muscle. Hell even 6 pm depending on how much he intakes during the day.
They have older kid diapers but you need a Rx, and only get these from your dr if you think he/ she will benifit from them.
Also look for a good made plastic cover the ones they make now are POS junky ones that my 2 yr old ripped with her own hands.
Most important let them know its not their fault (you'd be surprised how many kids/ adults think it's their fault and again it doesn't help them it makes it worse. Show them online how it's not medically their fault and explain genetics and how it works.)
I hope this helps, and just try and support them and empower them! Thats what they need. And of course your love when they accident not a mad or upset parent. This sends mixed signals to their brain and then you incur more accidents because you cause mental damage.
Also explain to him how he is not like his brother because of genetics and how his issues is because of quite possibly genetics and its no one's fault. And he may never be just like his brother explain to him their differences.
Good luck, and I hope this helps.