for alistar...or any tank, those are some of the worst powers in the game imo. leveling him up is the least exciting thing to me because of his style. a templar with shield equals the crappiest powers in the game. on the flip side its the easiest to manage.
warrior talents leave alot to be desired. Seems your best bet is passive talents in that tree.
Shield and Weapons tree. which is where u will want to focus most points. Look at anything thats an activated talent. your will have no choice but to waste points into passive or sustained talents (sustained are almost worthless for this type of player) to get the more powerful activated talents.
setup you tactics to use the activated talents in the appropriate situation. Remember that using sustained talents like threaten use up alot of stamina. When the stamina is all used up, your guy is fucked.
I suggest no more than 2 sustained talents for each member at least until u get more powerful. Focus more on the weapons talents rather than the warrior tree talents. The 2 handed weapon, archer and even duel weapon talents are the best in battle
you will also want to try and get the choicest spells for your mage. Problem is you dont know which are best and cant change it once u selected them.
here is a link for class specific talents and weapon talents for just tanks and archers (includes the awakenings stuff that wont be available to you in origins)
http://dragonage.wikia.com/wiki/Talents
here is a link for mages
http://dragonage.wikia.com/wiki/Mages
for a mage here is the best - imo
Blood Mage, Spirit Healer (get all 4 talents in both trees) - Arcane is great too, sub it for spirit if possible)
Arcane (the Purple ones, get all 4)
Primal Tree
Fire - (get all 4)
Skip Earth (although spells 4 then 2 in combination are deadly)
Cold - get all 4
Electrical (get 1-3...4 sucks)
Skip the creation tree….it blows and a spirit healer offers better stuff
Spirit Tree.
Skip the 1st and 2nd rows
Death – talents 1-3 (Priority)
Telekinesis (get all 4…crushing prison is a must! Combine force field with crushing prison
Skip Entropy….it has 1 or 2 good spells, but they are 4th row and the others are worthless.
Ok so that’s a lot of points and will take some time. But once u get there your mages will do devastating damage