How would I make a script that would run another script depending on who it is?

It's simply just an if statement and pieces of code. Here's some articles from Roblox that should help you find a solution: https://developer.roblox.com/en-us/api-reference/function/MarketplaceService/UserOwnsGamePassAsync / https://developer.roblox.com/en-us/api-reference/property/Player/UserId

You would use something like this, to check if they are a certain person:

local userids = {
    1234567,
    8901234,
}
game.Players.PlayerAdded:Connect(function(player)
    for i, v in pairs(userids) do
        if player.UserId == v then
            local script = game.ReplicatedStorage:FindFirstChild("script")
            script:Clone().Parent = player.PlayerScripts
        end
    end
end)

and you could use something like this to check if they have the gamepass

local MS = game:GetService("MarketplaceService")
local GamepassId = 1234567
game.Players.PlayerAdded:Connect(function(player)
    if MS:UserOwnsGamePassAsync(player.UserId, GamepassId) then
        local script = game.ReplicatedStorage:FindFirstChild("script")
        script:Clone().Parent = player.PlayerScripts
    end
end)

EDIT: to put the sword in someone's inventory you might do something like

local script = game.ReplicatedStorage:FindFirstChild("script")
script:Clone().Parent = player.PlayerScripts