How would I combine these 2 scripts without breaking it?

Combining the scripts will work as long as you do not try to create 1 variable name twice. Not doing this will cause the code after the second use to do what the second variable does. Putting two IsAdmins that are different in any part of the code will not work but if they are the same that is completely fine if you DON'T want to change what IsAdmin does in the code.

You would simply combine them! You would just need to rename any functions or variables that are the same so:

local speakers =    {"1337ZombieGamer", "Person2", "Person3"}
local banned =      {"Havemeat", "Username2", "Username3"}
local isAdmin = {["1337ZombieGamer"] = true}

local function checkSpeakers(name)
    for i,v in pairs(speakers) do
        if (string.upper(name) == string.upper(v)) then return true end
    end
    return false
end

local function banPlayer(banner, victim)
    if (victim ~= banner) then
        victim:Destroy()
    banned[victim.Name] = victim.Name
    end
end

local function matchPlayer(str)
    local result = nil
    local players = game.Players:GetPlayers()
    for i,v in pairs(game.Players:GetPlayers()) do
        if (string.find(string.lower(v.Name), str) == 1) then
        if (result ~= nil) then return nil end
            result = v
        end
    end
    return result
end

local function onChatted(msg, recipient, speaker)
    local source = string.lower(speaker.Name)
    msg = string.lower(msg)
    if (string.find(msg, "ban") == 1) then --- msg starts with "ban"
        -- words and numbers
        for word in msg:gmatch("%w+") do 
            local p = matchPlayer(word)
            if (p ~= nil) then
                banPlayer(speaker, p)
            end
        end
    end
end

local function onPlayerEntered(newPlayer)
    -- remove banned player if they try to come back in
    for i,v in pairs(banned) do
        if (v:lower() == newPlayer.Name:lower()) then
            newPlayer:Destroy()
        end
    end
    if checkSpeakers(newPlayer.Name) then
        newPlayer.Chatted:connect(function(msg, recipient) onChatted(msg, recipient, newPlayer) end) 
    end
end

game.Players.PlayerAdded:connect(onPlayerEntered)





function findPlayer(name)
    for _, player in ipairs(game.Players:GetPlayers()) do
        if player.Name:lower() == name:lower() then
            return player
        end
    end
end
    function onChatt(message, player) -- changes this name
    if message:sub(1, 5) == "Reset" and isAdmin[player.Name] then
    player.Character:BreakJoints()
        end
    end



game.Players.PlayerAdded:connect(function(player)
    player.Chatted:connect(function(message) onChatt(message, player) end)-- and here scene it -----was the same function
end)