Servo, servare has a variety of meanings. Saves is fine, but in many of these sentences "protects" or "guards" might be better.
regarding ille/illa/illud - i believe this course simply translates both ille/illa/illud and is/ea/id simply using he/she/it, so regular third person pronouns. i don't think English has a (more) fitting pronoun to translate it either, so we can't really make a distinction between them, and he/she/it works well enough. hoewever, closest in literal translation would "that" and "those" in some contexts be, and i think in this sentence "the father saves those" should be fine, too - or am in the wrong here?
We need an accusative case here - thus 'illos' whereas 'illi' is the nominative.
Sorry to bring this up once again, there is really no point in exercises over vocabulary which is not contained in the grammar section. NB I type my answers using the keyboard, not the word bank.