In a tweet, Mike Disa, the director of the WR reboot, said that if season 3 we would have seen that Dick the 3rd has 2 older siblings. So since we would never see them I made my own versions !
Both of them are way older than their little brother, one was an adult and the other a teenager when he was born, so they didn't get to truly bond with him since they were living their own lives when he was starting his, so even if he had siblings he mostly grew like an only child. They don't dislike him, they kind of like him, but he feels more like an aquaintance, a stranger even than a little brother. Mutual on his side of course, but that made him feel as lonely as ever while they at least had each other since their own age gap was of only 2 years (like all siblings of course they do fight but in the end they are very close). Yet like him they suffered from the arguments between their parents the times their father whom they watched on TV was home, fewer and fewer the older he was getting to almost never when Dick the 3rd was born (and that the 2 siblings were big enough to be good on their own as he thought in his subconscious, stupidly forgetting about the existence of his new one he was less used to but he just couldn't stand Delilah anymore), and like him they grew to resent their father for their own reasons, despite him once again loving them all but being too dumb to realize he hurt them. But unlike Dick the 3rd who got out of that experience depressed, self conscious, anxious and self loathing and ended up with an unsuccessful life in all aspects by the time of the reboot (lame at his job, job the job he wanted anyway, no love life...) and despite his denial and resentment for him still wanting to be like his father subconsciously, they would on the contrary have got out of that experience stronger, motivated and confident doing what they love fueled by a will to prove themselves and, on a subconscious level, bother their father. And in a way making their little brother feel even further like shit seeing how far they went
David Morgan Dastardly is the eldest, 48 (and still single and childless which has Delilah harrass him about) by the time of the reboot. He's now a dashing successful airline pilot, loving planes like his grandfather but being a Dastardly he does adds his twisted touch by purposefully piloting too fast, doing loopings, etc. The screams of the people inside are so fun ! And working there is fun, it's so expensive it basically robs them. Haha, poor people problems. Like his siblings he resents his father for an even more recent reason than them : David came out as ftm trans at 19 (reason for me he is not the one named Dick), after years of closet and denial he finally accepted himself as a man and started taking hormones. His siblings adapted immediatly, and even though it took a bit more time for Delilah who was used to have 2 daughters she ended up accepting it after a little while, now even mixing up her sons' names together instead of her daughters' (see Wacky Con). Dick the 2nd however doesn't take it seriously as proud as he is of his career and is still awfully albeit innocently ignorant on the matter and keeps referring to him as a she and often uses his deadname, because to him it is just a phase of his "big girl" who always was a tomboy to be "close to daddy". Irritates him beyond belief
Doris Richarda Dastardly is the middle child, 46 during the reboot, albeit to her mind and many others' she is still the youngest if Dick the 3rd doesn't count. She has a lot of blood on her hands because she is a mob boss owning a casino and from time to time does "freelance" job as a hitwoman. Lurking and surprising her victims all while not being noticed is even better than stealth missions in RPGs for her, those are more hobbies than a side job (but being a Dastardly she still demands to be highly paid lol). She had been married at some point, with some drug dealer she fancied, in Las Vegas one month after having met him. Lasted only 10 days until divorce but it has been enough to make her now 12 years old triplet daughters, Donna, Diana and Dana who are absolutely hellish, working like a creepy hivemind, on whoever babysits them, the terrors of their uncles and their mom's gangsters. She is a great feminist demanding for women to have the right to do whatever they want their bodies (she never shaves, plucks or waxes ; if her cousin Desdemona can grow a full masculine moustache why wouldn't she just let her own subtle grow ?!), that they can be stronger and more competent than men and don't need them for anything, using her own path, looks and homelife as an example. And what fueled her was a subconscious will to oppose her dad she resents who always was innocently mysoginistic to her and their mother (and David too), giving her dolls and pink things when she demanded toy cars and toy guns because those are girl things, those are what she wants. Sure he is proud of her career, but still thinks she should get married so that her husband would lead it better because those are men things. She is sometimes tempted to pull out her gun

Wacky Races © Hanna Barbera and Warner Bros
Drawing, idea, theories, David and Doris © me