Well, what actually happens here and now doesn't speak much to what is possible. Yes, I have to raise my voice, in fact, but it is possible that my children (actually only one and much bigger and stronger than I am) would behave themselves without this threat. So, it is obvious;
As I keep pointing out, the argument from evil is valid and no plausible arguments to make some premise of it false holds up.
But let's look at the basic argument. I'll do this fairly informally since it is easier to follow, but I'll try to put in all the steps.
There is a property, G, say, that amounts to "exists in all possible worlds". We need to take a fairly broad view of what worlds are possible, though not just "every state description" since that prejudges some issues, since, for every property, there is at least one state description in which nothing has that property, and, of course, we omit the empty world. I suppose that, to make things easier, we can assume that the list of individuals is transcendental, that is, that individuals are available to be referred to in various ways even if they have no properties in a given world (there are a dozen other ways to do this, but this is easiest -- and most generous -- for now). We also assume that all possible worlds are accessible from all other possible worlds.
So, premise: in this world, a, it is possible that something has the property G. That is, is, there is a world b in which there is a thing, g, say, of which it is true in b that it exists in every possible world. So, in particular, it is true in b that it exists in a. So, it is possible that the thing that exists in every possible world (has the property G) in b exists in this world, a, as well. But nothing in this guarantees that it has the property G in a, only that it is the same thing as has that property in b. Of course, this argument can be repeated for all possible worlds, so that it turns out to be necessary (i.e., true in all possible worlds) that it is possible that g exists in each possible world. But, more to the point, nothing here says that g actually does exist in any of these worlds, except b, of course, since 'g exists in c' is assumed true only in b and thus is only possible in c, for every world c other than b. So, it is (assuming that Gg is even possible) that Gg is necessarily possible. I haven't gone back into my misspent youth enough to recall or figure out what would happen if NPp => Np, but it looks to be a very strong modal claim and not one that can just be assumed to make this argument work (and the analogies all fail). The same applies to NPp => p directly.