Can they have free IVF when already have one child?

Hi My dad and his wife have been trying for a baby now for 4 years and it turns out my dad has low sperm count, my dad has me from a previous relationship (Im 23)nand his wife has a son from a previous relationship (he's 8). I know in the UK on NHS you can have your first attempt at IVF free, but will this still be free if they already have a a child? They havent got a child together and having a baby would mean the world to them :( they are so down at this moment in time, its awful seeing them like that! xx