Guardians of the Galaxy made it clear: Ronan wasn’t responsible for the deaths of Drax's wife and daughter; Thanos was. It was revealed at the end of James Gunn’s first MCU flick that Ronan was working for the Mad Titan when he killed Hovat and Kamaria. That prompted Drax to seek out and attempt to eliminate Ronan.
During their second encounter, Ronan admitted he’d killed Drax’s family. We assume that he was lying to mess with the Guardian's mind.
According to CBR, Kamaria is actually alive!
Drax (Comic Vine)
We should remind you that Gunn said that he would probably play around with the personal history of one of the Guardians in the series’ third installment.
Back to the CBR rumor…Kamaria (she had a different name in the comics, and later became Moondragon) isn't just alive and well; she’s actually found a new father. According to CBR, in Avengers: Infinity War, an enraged Drax will discover that the daughter he believed to be dead is the Black Order’s Proxima Midnight!
This isn't Thanos’ only connection with the Guardians. This reveal would lead to the realization that Gamora, Nebula, and Proxima Midnight are half-sisters, making the story even more interesting as an enraged Drax comes up with even more reasons to fight Thanos, and the sisters try to convince Proxima Midnight to follow in their footsteps.
But this is all just speculation.
Thanos (MCU Wikia)
We should mention one more thing: The twist would explain why Drax was the most underdeveloped Guardians of the Galaxy: Vol. 2 character; Marvel was trying to save the best for Avengers: Infinity War!
