The Todoroki family is one of the families in the show, but it’s unrelated to Dabi. There are some close similarities, but neither show has confirmed this connection, so there’s no real answer. For now, we have no information about how these two are related or who they’re connected to on any level at all.
The fact that both share similarities is very likely just a coincidence since much of what makes a character identifiable is by their appearance and abilities which often don’t relate to other characters sharing similar traits within different stories despite being based off of each other for inspiration purposes only (eg DC comics and Marvel). It comes down more heavily to where the individual person takes what they know from the inspiration source and what they apply their own spin on to make it their own.
In some cases there isn’t even a need for an actual connection between those sharing the same traits as readers project those connections on their own imagined terms altogether simply because that’s all they have to go off of, but it doesn’t mean that this is always the case either. Other times their connection is simply that they’re related, but not in any significant way.
All that’s known for the time being is that Dabi and Endeavor do share some notable similarities; however, it doesn’t automatically mean anything since there isn’t enough information out there at the moment to draw such a conclusion with any certainty yet. Endeavor being a possible connection between the two is merely speculative in nature, but only time will tell whether or not there’s any truth to it. Other than that, they may share some traits, but nothing has been definitively stated at this point so they could still just be coincidentally similar in appearance and abilities without being related after all.