Yes you are right it's a slippery slope but the laws of this country enable it to be slippery. If an intruder aggressively breaks into your home even with the ultimate intent of just stealing a box of tea bags, you can use deadly force to defend yourself against death, serious bodily injury (which includes broken bones etc), kidnapping etc as long as your fear is reasonable and the danger is imminent. This applies to every state in this nation - even the most liberal ones. And the reason why it almost completely impossible to prosecute someone under these conditions is because of what constitutes reasonable fear and imminent danger - it is completely arbitrary and impossible to disprove. Again, said intruder may have just wanted a box of tea - doesn't matter, how can you possibly know that? If someone breaks down your front door you have the right to be afraid, the right to assume imminent danger and as much as I hate to say this, the right to take a life. It's crazy but that's not my opinion dude - that's the law!
Now with this situation here is the wording of the law in Oklahoma with respect to self defense. By the way this below is with respect to justifiable homicide - which thankfully didn't happen but, pointing to your example, might change the way I saw the fight but almost certainly wouldn't in the eyes of the law.
"When committed in the lawful defense of such person or of another, when the person using force reasonably believes such force is necessary to prevent death or great bodily harm to himself or herself or another or to terminate or prevent the commission of a forcible felony"
This now comes back to a point I made earlier - the reality is these two brothers know they are themselves pretty good fighters but they have absolutely no idea of the capabilities of football Chad and his broski - how could they? Saying things like "what you got" clearly implies you must have something to bring to the table, so how does one possibly judge this. Especially when it looks like you already took one to the face (your bleeding nose) and then some idiot comes in and shoves you back 6ft in a very aggressive manor. There is no way to understand the ultimate intent at all - how does anyone know what Spencer Jones was or wasn't planning to do?
What I am saying is at the crux of why getting into any fight is just so stupid because you could find yourself dead based on the reasonable belief of what force is needed to protect oneself which is completely arbitrary and especially when that person is the defender and not the aggressor. Bottom line, just don't be an a$$hole and avoid the slippery slopes. Kind of simple no?
I talked a lawyer friend of mine about this today. He said the DA/prosecution will find it tough to get anywhere based on the above. These two kids just need to say they were terrified of getting their faces caved in by two bigger dudes who instigated the fight. He told me the one point they will get traction on is the force to "terminate" the commission of the felony - which is that point after Spencer Jones is in the choke hold and the guy jumps on him and just rains in the punches. But even then the fact that Jones tried to keep hitting the kid when he was on his back (really dumb to not just give up) may blow this angle up.
So to our San Diego State Aztec super-woke, bleeding heart liberal feeling bad for these bullies while enjoying life in the sunshine and surf of SoCal who delighted in how the "cops and DA are looking to prosecute" which matches their opinion - my friend also told me that any decent lawyer worth their salt can get these charges acquitted very easily and the only thing that would stop that would be some bias towards the plaintiff(s) based on the "hometown football hero" angle.
Once again, we are missing something really important here. Minding your own business very rarely starts fights which can end badly. Period.