Feanor looks too skinny here. Like I commented in others of your awesome illustrations the Noldor have pretty strong and proportioned bodies even in comparison to men. And Feanor was described as "great in mind and body beyond the measure of the Eldar"
I can picture this after the twins were born since she looks very tired-baring 7 sons can take a heavy toll even for the strongest of elf women. I love how he is so loving and supports her here. From what I see in the fandom I think most people think Feanor is incapable of loving anyone else except his father, but I believe he wasn't always a cold bastard and had been a loving husband and father before the lies of Morghot.
In General, I conceived that it Nerdanel in early pregnancy twins.)
I am sure that he loved his family. In the end, otherwise he wouldn't have as many followers. Well, actually, it is lies of Morgoth, the death of father and a misunderstanding of the Valar eventually brought him great madness..