@Wiimeiser  
Only for your headcanon.

This is wrong according to my age list:  
Derpy 24Y 5M 28D  
Dinky 9Y 6M 6D  
BonBon 20Y 6M 11D  
Twist 10Y 8M 13D  
If this was true, BonBon would’ve probably been pregnant with Twist in that particular scene, in fact, she’d be younger than Twist is now. In comparison, Derpy would’ve been about the same age as Motherly Scootaloo or slightly older when she had Dinky.

I’m a White guy with glasses, but I’m not related to Harry Truman.
 
Given how miniscule a connection between characters and appearances/associations/activies is necessary for this fandom to build instant backstory fanon– or, as with Derpy-Dinky, absolutely no connection whatsoever– I’m frankly surprised there aren’t any petitions going around to demand that Hasbro make TwistBon playsets and force DHX to include them as relatives in the show.

@Background Pony #F071
 
Look out! It’s the Fun police!

@Background Pony #F071  
They also both have special talents involving candy. So there’s that.

>They look somewhat similar because of using the same Flash model  
>OMG THEY’RE SISTERS!!!!
 
Headcanon gets less and less believable every day.

boring answer; Reuse of models
 
Interesting answer; Twist is Bons first born.

To whom?

Its looks like they only recolored her and replace her mane.

Or sisters or cousins or aunt and niece. Or even unrelated!