a.InjectFrom(b,c) is the same as doing a.InjectFrom(b).InjectFrom(c) the difference is that in the second case you can do a.InjectFrom(b).InjectFrom<MyInj>(c).InjectFrom(new MyInjwithParams(para), d) and so on.
of course you can do a.InjectFrom<MyInj>(b,c)
in your case for the simple fields you do:
and for your list there are many different ways, one very simple would be something like:
cDto.Countries = new List<CountryDto>();
foreach(c in country.Countries)
//go to repo/ service if needed
or you can do an injection that will do the same thing as above