خَالِدِينَ فِيهَا
...
Abiding therein,
means, they will settle there and never leave or move or die, they will never exit or wish to move to somewhere else.
This is like the Ayah,
وَأَمَّا الَّذِينَ سُعِدُواْ فَفِى الْجَنَّةِ خَـلِدِينَ فِيهَا مَا دَامَتِ السَّمَـوَتُ وَالاٌّرْضُ
And those who are blessed, they will be in Paradise, abiding therein for all the time that the heavens and the earth endure. (11:108)
...
حَسُنَتْ مُسْتَقَرًّا وَمُقَامًا
excellent it is as an abode, and as a place to rest in.
Its appearance is beautiful and it is a good place in which to rest and to dwell.
Then Allah says: