* If the paladin's focus is dead or friendly, assign focus to current target (beginning of every spell)
Dont believe you can see another targets focus (friendly or otherwise) - but you can cast against your pally's target. EG. priest: /cast [target=pally-target,exists,harm,nodead] Holy Fire
Paladin's spells will all become macro'd. First try to cast them on her target, if the target is hostile. If the target is friendly, cast them on her focus instead.
/cast [harm,nodead] Exorcism; [target=focus-target,exists,help,nodead] Holy Light;
* If the warlock's focus's target (paladin's target) is hostile, attack that
by "warlock's focus target" i assume you mean your locks focus ... /cast [target=focus,harm,nodead,nochaneling] shadowbolt
... if you are using a focus-based setup, then your focus would likely be whatever character you're playing at the moment, in which case: /cast [target=focus-target,harm,nodead,nochaneling] shadowbolt
* If the warlock's focus's target (paladin's target) is friendly, attack last target instead
*haven't tested this*
/cast [target=focus-target,harm,exists,nodead,nochaneling] shadowbolt;
/targetlastenemy
/cast [harm,exists,nodead,nochaneling] shadowbolt;

For healing spells, if her focus's target (paladin's target) is friendly, heal that. Otherwise heal her focus (the paladin, so I don't have to always have the paladin herself selected on the paladin to say "heal me")
/cast [target=focus-target,help,exists,nodead,nochaneling] Renew; [target=focus,help,nodead] Flash Heal;

Your language is a bit confusing tho, as you mention "the warlock's focus's target (paladin's target)" .. if the pally has a mob targetted, and the lock's focus was the mob (the pallys target) then the focus-target would be whatever the mob is attacking (ie. the pally) - and the warlock's focus-target would not be the paladin's target, as you describe it.

If you are setting the lock's focus to your pally, then you use [target=focus-target,harm,etc..] to attack the pally's target ...
If you are setting the lock's focus to the mob, then you use [target=focus,harm,etc...] to attack the pally's target ...