Small brood

Hello all, I’ve had a nest box up now for about 2 years. This year we’ve finally had a pair of blue tits come in, presumably male and female as the male has been very vocal when showing the female around the new home. Fast forward a few weeks and the nest is built.

Not a single sign of the male since the house hunting. Nest has been built and the female is often there. From the camera footage we can see only 2 eggs.

Is this usual for such a small number? I’ve read there is usually 8-14 but we are way off that. It’s been just under a week since the first egg. 
The female does leave the nest for a few hours each day which also worries me as during this time there is no incubation and also leads me to think the male has left her.

I think the chances of success are low with such a small brood.