DNS Monitoring Script Need Help

Hello.

I did small script using Netwatch to change DNS if have time out or larg time.
My issue its when 2 or more DNS down at same time the other script will add the 2nd dns which its also down.

is there is any way to add or remove only one DNS from IP DNS menu on scripting ?

My script

Netwatch to all DNSs with time out of 500ms of each DNS.

/tool netwatch
add down-script=222 host=208.67.222.222 interval=10s timeout=500ms up-script=DNS_UP
add down-script=220 host=208.67.220.220 interval=10s timeout=500ms up-script=DNS_UP
add down-script=8888 host=8.8.8.8 interval=10s timeout=500ms up-script=DNS_UP
add down-script=4221 host=4.2.2.1 interval=10s timeout=500ms up-script=DNS_UP

All DNSs UP

/system script
add name=DNS_UP  source="/ip dns set servers=208.67.220.220,208.67.222.222,8.8.8.8,4.2.2.1"

2-220 Down

/system script
add name=220  source="/ip dns set servers=208.67.222.222,8.8.8.8,4.2.2.1"

3-222 Down

/system script
add name=222  source="/ip dns set servers=208.67.220.220,8.8.8.8,4.2.2.1"

4-8888 Down

/system script
add name=8888  source="/ip dns set servers=208.67.220.220,208.67.222.222,4.2.2.1"

5-4222 Down

/system script
add name=4221  source="/ip dns set servers=208.67.220.220,208.67.222.222,8.8.8.8"