Confusing Link - Female assigned by her marital surname

[Rosinish]

I have a new Ancestry DNA match, I'll assign initials for ease of understanding/following...

F = 1st–2nd Cousin - 406 cM - 6% shared across 20 segments

F has 6 people in their tree - 5 living, 1 deceased, would be a g/mother who was known to me...
However, the tree has the g/mother with her marital surname rather than her maiden surname!

R = 1st–2nd Cousin - 578 cM - 8% shared across 21 segments

R has 6 people in their tree - all living.

I know R is a g/child of the above g/mother.

My question...is it likely going by DNA figures F & R are siblings or might they be 1st cousins?

From my paper trail & 1st hand knowledge (having contact with this family) - R comes up in my FTM as my 2C1R.

My g/m & R's g g/m were siblings.

Annie

[LizzieL]

My question...is it likely going by DNA figures F & R are siblings or might they be 1st cousins?

I think they could be either. You only have the DNA figures  for the match of F and R to yourself, which if I've read your post correctly is 2C1R to both of them. To know their relationship to each other you would have to know the level of their match to each other.

I have five people in my matches who share a grandfather (A), with quite a range of DNA matches to me:
R 112cM, E 52cM, S 49 cM, N 34 cM, G 34 cM

Without a tree and a paper trail, I couldn't tell that R, E and S are full siblings to each other (children of A's son) and N and G are full siblings to each other (children of A's daughter). R, E and S are, of course,  first cousins to N and G

[Rosinish]

I think they could be either. You only have the DNA figures  for the match of F and R to yourself, which if I've read your post correctly is 2C1R to both of them. To know their relationship to each other you would have to know the level of their match to each other.

Thanks LizzieL...

It's unfortunate Ancestry doesn't show how others match each other.

Annie