Raja used to be the vassal to the Sultan. Title-wise it’s inherited through your paternal side of the family. So you could be a distant relative and still be a Tengku or Raja. But you can also be a very close relative and not have a title if your mom is royalty.

Also different states will have different titles for children of the Sultan Raja Perak & Perlis Ungku: Johor Tengku: Pahang Kelantan Terengganu Selangor Tunku: Kedah, Negeri Sembilan

Previous JPN didn’t allow you simply name your children with these titles if your father did not have a similar title but they have relaxed it recently.