I like Grace Madeline and Grace Amelia!! i have a friend called Amelia Grace-personally I think it flows better that way.

Other names:

I noticed your aunt likes short, sharp and sweet names (Jack, Ben, Grace)
Here are some I like:

Rosie
Lara
Megan (on your list )
Zara
Hannah
Lily
Eve
May
Faith (Grace and Faith?)
Hope (Grace and Hope??)
Kate or Katie
Bella
Erin
Georgie

Longer names:

Emily
Isabel
Charlotte
Georgina
Annabel
Natalie
Keira
Olivia
Roseanna
Sophia
Bethany

Well- how about -

Grace Leigh
Grace Jayde
Grace anna
Grace Amie
Grace beth
Grace Frankie
Grace Racheal
Grace Erin

For twin two-

Grace and Caitlin
Grace and Amy
Grace and Amelle
Grace and Ellie
Grace and Lily
Grace and Marcy
Grace and Keisha
Grace and Kayley
Grace and Holly
Grace and Becca
Grace and Elisa
Grace and Sophia
Grace and Laurie
Grace and Charley
Grace and Ashlea
Grace and Ashlyn
Grace and Ashton
Grace and Christyl
Grace and Yazmin
Grace and Tazmin
Grace and Jasmine
Grace and Jessie
Grace and Jessmynda
Grace and Dawsyn
Grace and Emily
Grace and Niva
Grace and Emilyn
Grace and Amelia
Grace and Leah
Grace and Misha
Grace and Makynea
Grace and Nia
Grace and Makynlie
Grace and Taylor
Grace and Tylie

Hope i helped

Grace Josephine
Grace Madeline