SoupDragon,
Yes, after Landlord visit, we heard (not saw) him beat up the DMof2kids, kicking a hole in the door behind which DMof1kid was cowering with her DD.
Very distressing scene.
(TBH, I was worrying about how they film those type of scenes without traumatising the child actors). 
I, too, am completely confused about the family set-up there!
Initially suspected some sort of abduction scenario: that the younger woman had been enslaved/ abused by James (& elder woman?), and her baby the result.
But, as Smellbellina rightly pointed out, it seems like DCs no1 & no3 are elder woman's, and only DC no2 (the toddler) is hers.
She left at one point, didn't she, until James 'white vanned' her and brought her back. (Think she was off to her Mother's?).
So perhaps she was a fling who got pregnant, then for some bizarre reason allowed by elder woman to live with them (unpaid au pair/ household skivvy as 'punishment'?.
Think the 2 youngest kids are too close in age to make a surrogacy situation feasible?)
DC no3, the baby boy, must be either a genuine attempt by James at repairing the relationship with DW/DG
or
the twist is that younger woman is mother of DC no 1 as well as no 2? Oh, I'm lost.
Maybe they're all just into a ménage à trois.
Maybe handsome, Scouser, white van drivers are the new face of Mormonism.
(Though very probable that murder, violence, DA, extortion, adultery are frowned upon).