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Just off of first appearance I would say that they are macromphalus. The key characteristic to look at in regards to nautilus identification is the umbilicus, which is the inner 'coil' of the nautilus at the center of the shell. This is covered in some nautilus and not covered in others.
The striped pattern also appears to be different between those two species. I will double check the ID later today as soon as I can find my reference.
I'll second that - macromphalus (big bellybutton) has an open spiral - these look to be either pompilius or belauensis, and my understanding is that the major differentiating factor between the two is size - belauensis is typically much larger.
Having said that:
The stripe pattern and size is often totally different within the same species - here's a pic of two pompilius from the philippines and vanuatu: so basically I don't know. I would go with pompilius beacuse its more common than belauensis (IIRC)
Just remember that I measured from the longest point to the longest point, other specimens may not have been measured that way. As for the texture, there doesn't seem to be any 'cross-grid', rather they have 'bumps' running horizontally (horizontal in the bottom left picture in my first post). It also seems that the smaller one's (the one on the left) 'bumps' are raised quite a bit more than the larger shell (the one on the right).