I agree wth statement that Rina got dream team, but NOT for mage or paladin class
She have only 4 available kids intellect/spell oriented (Aislin, Nimbus, Sandro, Septienna ), and all off them give less bonus then 2 kids from Diana/Xeona. Also on that note Nimbus(18% intellect) and Nagash (24% mana , 84% gold) have to low bonuses
And as you said paladin have highest leadership now and it`s great, but neither glory nor holy rage works on undead, so he have high lds, but need to spend lots of magic runes to get to necromancy and utilise undead army, and lots of might runes for dark commander to make them movable.
My thought is that warrior would be best class for all undead army. Dark commander easy, and magic runes he get only thing he needs is really necromancy skill, no need for to much upgrading other magic tree skills.
As for best kids Moandor is great if necromant rise undead is permanent like necromancy spell (if not then you dont need huge number of them, only 1 will be enough to cast plague on start of battle and that`s it for them. Death Hart and Vidomina are great -15%lds for all and -21%for bone dragons, but i would pick Vokial over Tamika regardless how crazy it seems (that +6%dmg and +1poison dmg would be great if you lead thousands of skeletons and spiders, but for leading bone dragons, 2*vampires, black knights, necromants that +dmg is not so much). And Vokial gives +24% attack for necromants not 24%dmg = 3 dmg for 1 unit in army.
With Haart, Vidomina, Vokial, Moandor and 3rd lvl necromancy you`ll have -31% for all undead and more reduction for vampires, necromants and bone dragons. All in all nice team build But to limiting, since only bonus you get next to lds reduction and little boost for those 4 troops. No hp bonus, resistances, moral etc like for living units with other kids.
All in all Rina is interesting for playing, but you get her on start when there are no undead available, and even those you can find are total crap (some zombies, and skeletons in Marshan swamp with no way of keeping them alive). If there`s way to upgrade Rina or something like that once you get to undead lands beyond Elven territory it would be great to keep her, beyond that she`s not much of a keeper