Disable/remove third party cookies from website

Question

I need to add a cookie consent system on our website due to GDPR laws. Currently everything is set to disable and enable the cookies, but I can't seem to delete third party cookies which are created by Google Analytics or AddThis (some social media tracking), because I can't find them with document.cookie.

So does anybody know what the best option is to either:

1. Delete the third party cookies
2. Prevent the scripts from running at start and launch the script after the user consents
3. Run the scripts from the start, but unload the scripts if the user declines the usage of cookies

But just to be clear, I know how to remove regular cookies, I really need to find a way to remove the third party cookies or prevent them from being loaded (yet make sure they load when the user wants it)

<script type="text/javascript" src="//s7.addthis.com/js/300/addthis_widget.js#pubid=ra-556d15415fgddz4536" async="async"></script>

<script>
function enableCookies() {
    console.log('enable cookies');
}

function disableCookies() {
    console.log('disable cookies');
}

window.cookieconsent.initialise({
    onInitialise: function (status) {
        var type = this.options.type;
        var didConsent = this.hasConsented();
        if (type == 'opt-in' && didConsent) {
            enableCookies();
        }
        if (type == 'opt-out' && !didConsent) {
            disableCookies()
        }
    },
    onStatusChange: function (status, chosenBefore) {
        var type = this.options.type;
        var didConsent = this.hasConsented();
        if (type == 'opt-in' && didConsent) {
            enableCookies();
        }
        if (type == 'opt-out' && !didConsent) {
            disableCookies()
        }
    },
    onRevokeChoice: function () {
        var type = this.options.type;
        if (type == 'opt-in') {
            disableCookies()
        }
        if (type == 'opt-out') {
            enableCookies();
        }
    }
    position: "bottom-left",
    type: "opt-out"
});
</script>