In skyrim elderscrolls is it possible to bring back npc's?

Go to a save prior to the killings. Or better Restart the game.

Once dead a named (Human) NPC will be dead, No respawning. [various generic bandits/thugs will respawn anytime after three days.]

Regarding the materials, in Riverwood under the work bench you should find Iron and steel ingots. If you followed the Imperial in to the village they are free, if you followed the Stormcloak in you will have to steal them.

Markarth blacksmith has a wooden crate that has ingots.

Carry a pickaxe as you roam the country so can mine ore deposits when you come across them.

Buy materials at all the Smithy's. Forge only New Expensive items. Do not upgrade (at the early times) anything except New Forged items. Especially any item of less than 35 gold value.

Also, to make money Enchant items. It will be expensive to get going but is well worth it later.

In the early days use the barrel next to the Forge to store materials, BUT be warned you must visit that barrel everyday or lose the contents to spawning resets.

Hunt for pelts.

Get a Follower to assist, as a mule to carry loot and to protect the Dragonborn. Sell the cheap stuff to buy material.

Tip: Do Not Level Up too quickly or the Foes will out fight you.

It is very enticing to raise the levels for smithy and enchanting, but you must first consider your Health and Combat abilities. Being master of Smith/Enchant will not serve you if you die because you forgot to learn combat skills.

Archery, Sneak, One weapon class. One Armour class, meaning do Not spread your valuable Perks around willy-nilly. Plan your "education". Survive first,

In addition to the excellent answers given, I'd add that there are blacksmiths in other towns (Dawnstar, Riften, Solitude, Windhelm, Shor's Stone, Falkreath, and Markarth has two). You're not restricted to Riverwood and Whiterun. Take the carriage to other towns, if you don't want to travel by foot. Balimund in Riften has a lot of stuff in his house, in the basement.

Named NPCs do not respawn, though some of them do have "seconds" who will take over their shops if they die, and should have the same inventory as the original merchant. There's lots of iron to be mined at Halted Stream Camp north of Whiterun. Might want to take a follower with you.

In future, you should carry a few cure disease potions and check your "active effects" list for diseases every day, or after fighting vampires, getting wounded by traps, or bitten by animals. You can cure vampirism with a potion if you catch it within the first 24 hours.

Find out their (I think it's BaseID, otherwise it's RefID) ID and type in the command (the ~ button)

Prid (the ID goes here)

moveto player

resurrect

and voila~ they should come to life, if any step doesn't work, try using the other ID

You can make iron ingots by collecting the ore and using it at a furnace in one of the larger cities. By the way, you may have more luck at uesp.net

is it pc or console.? if its pc you can open up console by hitting this ~ and typing this in, Try typing this on the console:

help "npc name" 0

press enter

bunch of codes will appear bunch just find the one that has a label NPC_ on it.

then do this type

player.placeatme <-NPC CODE->

if its console then you have to reload the save.