Is it a requirement for witnesses to know the names of the assailants?

Witnesses need not know the names of the assailants, as long as they recognize the latter’s faces. What is imperative is that, on the basis of their personal knowledge, the witnesses are positive as to the physical identification of the perpetrators. (People v. Sorila, Jr., 578 Phil. 931 [2008]).

Thus, it was sufficient that the witnesses were able to identify the accused in the crime scene and when they took the witness stand. 

What are the requisites that the prosecution must prove in a murder charge?

For the charge of murder to prosper, the prosecution must prove the following: (1) the offender killed the victim, and (2) the killing was done through treachery, or by any of the five other qualifying circumstances, duly alleged in the Information.  (People v. Gabrino,G.R. No. 189981, 9 March 2011, 645 SCRA 187.)