Hmmm yeah i would say they get along fine, i think the friction between them would mostly be from the sheer difference of their inherited nidhogg, which nadir's is the sources so directly tied to estinien and ennius and not entirely corrupted like how kamuis is inside of Amelia . Very much Amelia brain: but if i was able to eat her nidhogg i can be double nidhogg . :)

Meanwhile Nadir would probably have the rivalry of it instead of wanting to consume for power.

(Though older i have Faust feeling like the inferior one of the 3 because of how Amelia has something that directly is tied to their deceased father(kamui) and Nadir also has something from him too (nidhogg) but Faust has. Nothing to remind him of his dad. )

I think they'd both be foodies, they like eating a lot of different foods from different places and Nadir would let Amelia dress her up cause she doesn't care about fashion (Nadir and Faust would be more close than Amelia and Nadir in that canon)