Can you please help translate this for me, thank you

Denise and her boyfreind not going Istanbul they go Antalya.

"Denise ve erkek arkadaşı İstanbul'a gitmiyorlar; Anlatya'ya gidiyorlar."

In this sentence "onun" (her) can be omited since arkadaş+ı already has the possessive suffix for 'her'.

Istanbul'a (to Istanbul) and Antalya'ya (to Antalya) have the dative case suffix. The dative case suffix has two forms which are -e and -a.

1. use -a if the last vowel is a,ı,o,u
2. use -e if the last vowel is e,i,ö,ü
3. On number 2 and 3 if the last vowel is also the last letter (if the word ends with a vowel) then add the buffer letter -y in between since we don't put two vowels next to each other.

There is an exception to number 3 where the buffer letter changes from -y to -n if there is a possessive suffix used. In noun modifications possessive suffixes are used.

Example:
İş Bankası > İş Bankasına
Kuşadası > Kuşadası'na

Thaky you so much, that's a great help