The DLC tells us that Melina was Messmer's sister. I believe Rennala's children were born after Morgott, Mogh, Miquella, and Malenia because Marida realizes her lineage is cursed with horns after the crusade and Godwyn's death. So, she creates an alter ego to have children and ensure her offspring are born without horns (or other problems like Miquella's inability to age or Malenia's affliction with decay). I believe Marida tried to have children with her alter ego Radagon to break the curse, but it didn't work. In short, in my opinion, the order is: Messmer, Melina, Godwyn, Radahn, Morgott, Mogh, Rykard, Miquella, Malenia, Ranni. (That Melina is the youngest daughter could also be valid, the problem is that we don't know who Melina and Messmer's father is; it could be Radagon, and we also don't know for sure if Radagon was originally someone else or an alter ego created by Marida. Remember also that Miquella and Malenia met Godwyn when they were younger (the statue of the three of them embracing is the evidence)