Judging from all available recourses even bayonetta which suggests both games are in the same universe and that Eva is actually one of the Umbra witches and made a “pack” with Sparda to which she gave him the time bangle which is also in the first DMC game, this is what we know,
Sparda
He put all his demonic power in his sword to seal Hell, then left with his 2 swords rebellion and Yamato, he continues to fight demons in the human world and rules in fortuna, then he marries and has twin sons who are half bloods, but how if he drained all his power, it’s because he’s still a demon, he also left before their 8th birthday and disappeared?
he might of died of old age or might have been captured judging we can assume DmC has some truths like adding the mansion and portrait in DMC 5 but we will never know until...DMC 6 (S) for Sparda!
Sparda
He put all his demonic power in his sword to seal Hell, then left with his 2 swords rebellion and Yamato, he continues to fight demons in the human world and rules in fortuna, then he marries and has twin sons who are half bloods, but how if he drained all his power, it’s because he’s still a demon, he also left before their 8th birthday and disappeared?
he might of died of old age or might have been captured judging we can assume DmC has some truths like adding the mansion and portrait in DMC 5 but we will never know until...DMC 6 (S) for Sparda!