I’m not sure how to make it work how you have laid out. But I would do the check in the jinja template anyway. Get your current ntp lines. In the jinja template run.
{% for ntp_server in ntp_config_get %}
{% if ntp_line not in ntp_servers %}
no ntp server {{ ntp_server }}
{% ending %}
{% for ntp_srv in ntp_servers %}
ntp server {{ ntp_srv }}
{% endfor %}
If you got the whole line of current ntp servers, you’ll have to parse the ips with regex, I’m certain I’ve done something very similar to this before. Let me know if you still have issues after trying this.