How do I get though this Bugged Skyrim Main Quest?

I'm up to Diplomantic Immunity but it keeps bugging out, when I get into the embassy I go inside and none of the NPCs are the apart from a guard, that guy who was outside with me, the elf who's hosting the party and a woman serving drinks

what I did before going into this mission was that after I killed the dragon with Delphine I let her return to Riverwood and I went to Windhelm to join the rebellion and get the house there since it was the biggest and all the housing mods suck since they all contain game crashing bugs, then I saved in a new file just before I started the mission before telling my companion to leave just in case if I couldn't find them again I could just follow them

I've completed this quest before in version 1 so I know that it shouldn't be doing this and it's horrid programming on Bethesda if the bug is being cause by the fact that I spent so much time before it doing side quests building up my skills and arsenal (if a game bugs a main event like this and the cause was from doing side events then the game should be considered a failure in all regards)

I looked up on the wiki seeing if there was a way to get passed this but it said I have to restart, im not sure what that means, I know that I can use a command in the console like "SetStage CWMission04 200" (that's a fix to work around a bug for one of the Stormcloak Quests) and it soulds about right cause I use a similiar command in Oblivion for one of the Quest Mods to start it without having to complete the game (much rather having the gates to explore and clear out) but I only know this command from using Oblivion's editor and I don't have Skyrims (so I'm not sure what the mission or stage arguments I need to just skip to the part where I can begin the infiltration of the embassy

Does anyone know how I can get though, i quit playing Skyrim before because the first version kept crashing every half an hour and that was without mods and if I have start a brand new game I think I'm just going to give up on Skyrim and consider it worse than Morrowind that when you get to a certain point you have to continue doing the main quest line otherwise if you take to long to return to it it'll skip though most of it

(NOTE: I do have multiple save but I only save a new file when one of the Main Quests end and I get given another to which I save on a new file and do a bunch of side quests, I could just load a previous one but that would mean loosing out on the hours of gameplay I just put into the side quests for just Windhelm and Windholds to which I am in a middle of a few)