Ok, Ugily's advice is on the dot but you still have a long way to go with Necro, so i'll focus on Rogue since she is further in and you could hand down some items to the Necro with her.
Golem is a spell that summons a minion, it is slow but does physical damage, and is used to agroe mobs and keeps them off you, he also gets a bit better in higher difficulties but he is not a tank, he's mostly distraction.
Since you are still in Normal, the Arctic set is stellar if you have it, if not focus on finding a good bow like i suggested, with as low Attack Time as possible (check Attack page of Character screen). If you killed Lazarus in a previous game it means you have 1 hour to beat Diablo before he reaches full power, and we don't want that. So use the waypoint for Hell lvl 16, look around a bit for an area with red glow, this is where the portal to Unholy Altar is, and below it the entrance to Terror's Domain, if it's not near the waypoint use Warp and check near the stairway up to Hell lvl 15, if not there restart game until you find the entrance to Terror's Domain fast, time is crucial, don't bother with any monster on Hell lvl 16, your focus should be to just get to Terror's Domain as fast as possible, by Teleport most likely. And once here open TP and if you die and return don't forget to open a new TP.
In Terror's Domain start by clearing the West room, but don't agro too much from South room (you don't need to clear it), them move up to clear the East room and lastly the North room, then unleash Doomlord Gam'ar, keep summoning Golem a bit behind him so he turns away from you and hits the Golem, and while hitting him keep moving back to the cleared rooms and at need Teleport to safety out of sight, he will follow you but the minions from his portals won't and will remain stationary in the rooms if they don't have sight of you. He is the toughest of Diablo's generals, and immune to Magic (unfortunately Bone Spirit) and also does a ton of damage with his Arcane Spiral (i made this name up for his nova spell) so don't be in close range to him.
Once defeated clear the middle way and get to the East room, don't step to far in just enough to get sight of Bloodlord the Destroyer, he will teleport on you and likely kill you, he is a bit difficult to beat because you don't have to be more than a few squares away for him to teleport on you, so you kinda have to dance with him. Thus we need to keep the Golem up at all times, so he stays near him, shift click to attack (Bone Spirit on LMB work too to whiter him down) and keep your cursor over the Golem to see his health and once low health summon new Golem about 2 squares away from Bloodlord the Destroyer, so he spends some time moving towards him.
Now move to the West room, and have MultiShot ready on LMB since Benedict the Black summons several skeletons, Teleport on RMB and follow him around as he teleports, he doesn't have much health so shouldn't be a problem. Once done with him open TP here and destroy the 3 crucifixes in his room, then head on to the South room where Diablo will spawn, don't worry he will clear the room when he spawns, so it will be empty.
For Diablo you need a ton of potions, preferably 25(belt)+40(inventory) Full Rejuvenation, if not mostly Full Mana, and use the wall from his room/middle area, use MultiShot on the area he will come from, because the angle is good and many shots will hit him at once. Teleport to the safety on the other side of the wall once he gets too close. That's about it, you will need a few tries to get the muscle memory and timing right but it will make you a better player. If he reaches full power he becomes much faster/tougher/aggresive and it's best to just restart the game and try again, the 1h timer will also reset. Before you restart don't forget to pick up what dropped from monsters in his level, until now you should't have bothered picking up anything since you need to kill him in 1h.
Further down in this topic is a pic explaining how to use the wall:
http://awake.diablo1.eu.org/necromancer ... t1090.html