Hadith query

Q: Is it true that there is a hadith stating something to this effect: "Only ambiyaa are allowed to be buried in structures." If it is a صحيح حديث then why are the two khalifas (hazrat Abu-bakr and hazrat umar) buried in a structure?

Consuming haraam

Q: If a person were to consume haraam food eg. a chocolate without any doubt or without knowledge that it contains haraam, would a person's imaan be weakened? Similarly eating take aways.

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?