Names, Surnames & Titles

Keeping two names

Q:

1) When 2 names are kept, eg Faathimah Zahraa, then is it fine -or not advisable- to call by only one of the names at times. Eg calling the child sometimes by both names, sometimes only faathimah, sometimes zahraa, is this fine?

2) When calling by both names together, would it be pronounced Faathima-tuz-zahraa', or Faathimah zahraa', or would both be fine to say?

The name "Raju"

Q: A male whose name is Raju, what does the name Raju mean? Is it permissible to keep the name or should the name Raju be changed because I
heard Raju is a Hindu name?

The name "Alayna"

Q: Is it permissible to keep the name alayna الينة as in the root ل ي ن not علينا the preposition. Alayna is derived from layyinah which is mentioned in surah taha. Alayna is also mentioned in surah yaseen. Is Aleena or liyana suitable names?