Good thinking!

But what if you were already in country B, not your home country, be it on holiday or anything else?

einherjer

First move family into safety. This usually means outside of the city.

If flights are N/A, then we need to cross borders to escape, then I'd choose the most feasible crossing and attempt to cross.

bitcoin

Acting decisively on incomplete information - a thought experiment for you!

First move family into safety. This usually means outside of the city. 
Now it really depends on specifics 
- light pack the family as fast as possible 
- if I don't have a car, try getting a good driver 
- if there are fights in the street, try getting the most up to date locations and strategize/predict the development 
- if it's "your hometown is under attack by another country as part of war" type of situation, then I'd immediately (after family safe) start helping with preparations for home defense (blocking roads, barricades, molotovs)
- ... again, it really depends on what is specifically happening, what needs reaction 

If flights are N/A, then we need to cross borders to escape, then I'd choose the most feasible crossing and attempt to cross.