You could say “My doctor recommended I limit my eating window each day to help with my (insert any condition here).” For some people, if the doctor told you to do it, there’s no higher authority.
I don’t know how long your fasts are, but you could try to work a meal in around them. If you know your family wants to do dinner, move your eating window for the day.
Do you have a history of eating disorders or mental health issues? That’s going to be a tough bar to clear, since your family is acting out of concern but doesn’t understand this whole other way of living.
This is more on the “relationship” side than “fasting,” but as a person moves away from the time(s)/situation(s) where that high-alert status was perhaps appropriate, their friends and family do need to learn to themselves heal and dial it back to a more typical level so the person can live their life. IF is a reasonable choice for a person to make. It’s okay to just hold a boundary like “this is what I’m doing and I understand that it worries you but your concern is in this case misplaced, please respect that and trust me that I am being safe.”
Use it as a tool, if they invite you out then you can make that day an omad day.
If they invite you out too often then go to some and on other just say your dieting and they already ate takeout this week so your gonna skip this one.
I’m doing alternate day for November and find it easy enough or if you want to eat every day omad or a 20:4 eating window could be a good alternative.