If you're on Negligence, you'll need to use Donoghue v Stevenson, and also the Caparo test.
For the drunk driver, you need to establish, using Donoghue if he: Owed a duty of care, breached that duty, and caused damages. To find if he owed a duty you have to use the Caparo test which is: 1) Did the driver have a relationship of proximity with the two people he injured? 2) Are the injuries he caused foreseeable? 3) And is it just and reasonable to impose a duty of care?
-- that would be 1) Yes, by using the public highway, he would immediately create a relationship of proximity to other road users such as pedestrians, as he would have them in contemplation, e.g if the claimant was far away and obscured as in Bourhill v Young, proximity might not be produced 2) Yes, it is foreseeable by driving drunk in a broken car that he might veer off and injure someone, just like in Kent v Griffiths where it was foreseeable that an ambulance delay would cause injury. 3) Yes it is reasonable to impose a duty of care, unless for public benefit the duty should not be owed as in Hill v w/yorkshire cc.
He would have breached his duty under the "reasonable man test" established in Blithe v Birmingham, which is an objective test to find if the defendant committed any acts or omissions that a reasonable man would not do. If your driver was a professional driver, his standard of duty is as high as other professionals in his field, as in Bolam v Friern, where withdrawing relaxant drugs from the patient in electroconvulsive therapy was an agreed upon method, making the doctor not liable for the fractured jaw. On the other hand, if your driver was a fifteen year old girl, he may have a lower duty of care as in Mullins v Richards, where the injury from a fractured ruler, although would not be expected from a reasonable man, might be expected from a child. In any case, by driving drunk in a bust car he did what a reasonable man would not do, and so he breached.
And lastly, it was due to the breach that damages were caused. it must be established factually and legally that the cause of damages to the two people was from the driver. For factual, the but-for test can be used, as in Barnett v Chelsea, where the claimant’s death was not due to the doctor’s negligence, as he would have died anyway. Legal causation too needs to be established. For this, damages must not be too remote, like the burnt wharf in the Wagon Mound was too remote, but the immediate oil spills were not. In this case damages were probably not too remote. However, it could be that there was a Novus Actus Interveniens under acts of the claimants themselves. If they were, for example, standing in the middle of the road practicing a dance routine or something, this could break the causation, as in McKew v Holland where the claimant broke his ankle after jumping down the stairs after his leg gave way. That Novus broke the legal causation by an act of the claimant himself.
Hope this helps