It's a sad situation- my condolences. However the tragedy, and the tattoos are not relative. You are saying that because your bro and his wife got matching tattoos, everyone is ignorant and generalizing... because their son passed away? Because they underwent a horrible experience that means they are automatically not douchbags?
I have experienced suffering like your bro and his wife, but never desired a tattoo. Not to say your bro is a douch, just that that his personality has nothing to do with the situation.
They want to be reminded of such a painful experience for the rest of their lives? How is that honouring their son? Their son would want them to be happy in life, not wake up every day and be pained every time I see my tattoo, and reminded how I felt when I got the tattoo. It either becomes a negative symbol, or just a symbol that is on your skin for the rest of your life. Either way it has no bearing.
My old neighbors got tattoos of their dog who passed away. That must've mean they dearly loved their dog that they etched her name in their skin forever?? Actually they treated the dog like trash while living. She was a street dog that depended on food from the neighbourhood folks. The tattoo and the purpose for it are irrelevant, and serve more as self-validation than anything else.