How do I force my computers to always use the DNS I designate?

Windows 10 Home Edition. Family computer not part of a network or group.

In order to block inappropriate websites I log in on my own administrator account and I set the DNS in adapter settings to a family safe DNS service (in my case OpenDNS Family Shield, primary 208.67.222.123. and secondary 208.67.220.123) instead of “automatically use DNS option.” I then set my children as standard users so they have no access to these settings.

However there are two problems:

  1. We use cellular hotspots for connectivity (in essence these are our ISPs). I noticed that AT&T hotspots obey but Verizon hotspots just bypass and use their own DNS. How could I force my PC to use my preferred DNS always? I have no way of changing settings on the actual hotspots.
  2. Every once in a while the setting of the computer will revert back to “automatically assign DNS” thus entirely uprooting my whole plan.

How can I fix this?