The Hoor Al-'Ayn (damsels of Paradise), are they like the angels in that they cannot sin, or are they like humans? And if so, then how are they deserving to be in Paradise?

All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.

First of all, our advice to you is to ask only about matters that benefit you in your religion and what requires action and to refrain from raising such odd and pointless questions.

The Hoor Al-‘Een are definitely not angels, nor are they humans. Rather, as the scholars said, "They belong to a different species created by Allah, and they were not born ... They are not descendants of Aadam (Adam), may Allah exalt his mention; rather, they are from a different species..." [Fat-h Al-Bayaan: excerpted with slight modification]

The Hoor Al-‘Een are a special species that Allah created to honor the people of Paradise and to derive pleasure from them. So there is no room for asking whether they sin or not! Paradise is not an abode of religious assignment. There is also no room for asking about their deserving to be in Paradise.

Allah knows best.