You know, one of the biggest problems or at least one of the issues for my "Marcone is Harry and Murphy's son theory" is the durability of Marcone's birth in multiple alternate realities. They'd require that both Harry and Murphy survive in many different realities. And, that they have some relationship where they get it on and conceive of Marcone. And that, in some fashion involving time travel, Marcone is placed in a contemporary timeline of his parents. The Dresdenverse would then further allow for 'safe' paradoxes, contradictions that arise from event interactions between out of linear sequence actions made by father, son, mother. We do know though that Marcone and Harry often directly impact life/death of the other. Marcone even mentions poking Fate in the eye I think in Dead Beat when he helps save Harry from Corpsetaker after Gard had mentioned it was Harry's fate to die that day.
This theory about Marcone being descended from both Harry and Murphy has some but limited circumstantial evidence but it mainly exists as an artisticly desired plot point on my part.
As to the splinters, time loops, and divergent timelines, I think they can all be included in the Dresdenverse.
1) There is free will choice that causes changes in the timeline. Much evidence in the form of WOJ and spoilers about Mirror Mirror support this idea.
2) We know it takes lots of juice to change particular things per conservation of history in Cold Days, so that is the mechanism where stable time loops or an unbroken timeline would occur.
3) Again from Vadderung, we have evidence that suggest time travel can cause splintered timelines that arise from free willed choices with time travel in the mix. AKA, Harry goes back in time to kill his grandfather. This is time travel, check. This is free willed choice, check. This is paradox if Harry is successful, check. Then a branch at that moment spins off with his grandfather dying off right then and there so who knows what that branch looks like. We however do know mostly what the branch looks like where he is unsuccessful in killing off his grandfather. There might be some alterations though with his grandfather learning about his grandson coming back in time to off him and subsequent effects (feedback) of this knowledge may have back up the branch. There would like be some time loop'ish equation going on until a steady state equation would be reached.