But succession in Rome is not so rigid, and nothing would technically prevent two emperors from ruling together, I’m not saying Commodus would rule alone, but he’d certainly co-rule with Verus, if Aurelius predeceased both of them. Aurelius in OTL probably meant to name both Pompeianus and Commodus as co-heirs, so that the former could serve as guidance to the latter, but since Pompeianus refused he opted to let Commodus rule alone while surrounded with all his advisors and friends. There’s no Roman emperor who ever willingly ignored his own son for the succession, why would Marcus Aurelius of all people, especially since the relationship between father and son seems to have been amiable?
Of course, if Verus and Commodus end up co-ruling, Lucilla will surely try to murder Commodus. Wheter the two men will still be in agreement, or wheter one would murder the other is not for us to know.