i believe that Ranni and Melina are twins of a sort (same spirit 2 bodies) since Radagon and Marika are the same being. the union between Radagon and Rennala woulds also have to involve Marika. so that could make Melina Marika and Rennala's daughter. also makes sense why she died. When the whole act of Ranni's took place she killed not only her own body but her twins also.

Amy definitely stands out - I get the adoption part, so that's fine that it doesn't fit. Amy is an enigma.

I honestly dont know why Amy is named Amy, but what I do know is that Polyanna is adopted. Anyways the original parents (Godfrey, Rennala, Radagon, Marika) go by those initials

They are all "G R R M" until Malenia's children, oddly enough

There wasn't an easy way to portray Godrick, and there were plenty of generations separating the two. Malenia's children on the other hand are implied to have been born from the scarlet rot itself. They are sort of like her clones I guess.

Who did Malenia and Godwyn have a child with?

Basically nothing at all is written about Godefroy, so I didn't add him to this list. My working theory is that Godefroy is the spirit of the disgraced Godrick, since he is such an embarrassment. There is also some more cut content that I left out of this- for instance, a cut storyline of Gostoc being Godrick's son.

What about Godefroy? Is there anything on him?

Yeah, she heavily implies via dialogue that she is Marika's daughter, and also her name in the game files is MarikaofDaughter

Melina?