Twinkle Seas popped against a Soul Whisper shown, Marble Magic hid. So it is at least dominant to Marble Magic
It would take several proofs to show Custard had Marble Magic hid (a pain because parents on both sides have soul whisper shown and marble magic hid and I don't know which gave her the hid) but will show all the proofs if necessary.
I thought it would be simpler to pop the hid on the twinkle seas kid to see if it is soul whisper or marble magic as that would be more informative I think.