Sometimes when they argue, it takes many times of putting them on top of each other (15-20 even) to get them to try for a baby. I don't know it matters, but I take turns--put him on her then her on him. Eventually, they will give in. Just be persistent--you are ultimately in control, lol.

NOTE: Before you keep trying when they argue, make sure both are fed and showered. If either are "not feeling fresh" put them in the shower. Not sure if that helps with babymaking, but I do it anyway. I like to think that if they are clean and have full tummies, they will be in a better mood to try for a baby.