Is merely thinking about the fiancé's sister, and the accompanying feeling of fear of envy or the evil eye, considered envy? And how can one get rid of these thoughts? And does reciting the Mu'awwidhat (Surahs Al-Falaq and An-Nas) protect from the evil eye even with the presence of these thoughts?

The enquirer is advised to divert their thoughts from the issue of the evil eye and instead occupy their time with learning, inviting others to Allah, and serving their family. The mere thought of your sister does not mean she has been afflicted by the evil eye. Praying for her with blessings and saying: "What Allah wills (has happened), there is no power except with Allah" is sufficient for her safety. So, if any of you sees something admirable in his brother, let him invoke blessings upon him (i.e., pray for blessings upon him), as the Prophet, peace and blessings be upon him, said: "What prevents one of you, if he sees something he admires in his brother, regarding himself or his wealth, from invoking blessings upon him, for indeed the evil eye is true?" And among the ways to repel affliction by the evil eye is saying: "What Allah wills (has happened), there is no power except with Allah." Some of the predecessors said: "Whoever is pleased with something from his wealth or child, let him say: 'What Allah wills (has happened), there is no power except with Allah.'"