Additional Document for visa D

Hi Guys
I’m from Non EU country , got married and also have two sons from my Irish wife . Last year September I applied for Ireland visa to join my family . On Monday I got an email from INIS requesting for my second son birth certificate which I sent to them same day . because my wife was pregnant when I applied the visa. Please I want to know, asking for additional Document means I will get the visa and also how long it will take before they will approve the visa .