Word Usage – My Family is Vegetarian or My Family are Vegetarians?

Yes, but ...

Saying "excuse him" is usually patronizing, implying that the other person is not responsible or polite enough to make his own apologies. If you're talking about a child, "Oh, please excuse my son, he doesn't know any better", well, we expect children to not be responsible. But if you say it about someone else, "Please excuse Fred", that's almost certainly insulting to Fred.

It may be, of course, that your intent is to say that Fred is irresponsible or rude, in which case "excuse him" would be totally appropriate.

The one example I can think of where it would not be insulting would be if the person could not be expected to know that something he did was inappropriate. Like, "Oh, please excuse Fred. He's still learning English, he didn't mean that statement the way it sounded."

The rule says to use the plural to mean either "all" or "any" of that thing. You have to figure out which of these from the context.

Someone ate the donuts (they ate all the donuts that were in a particular place)

I bought us donuts (I bought some quantity of donuts)

She hates donuts (She does not like (to eat) donuts of any kind)

Basic logic applies here. If a man has three apples and you say "The man is eating apples" it would be silly to assume he's eating all the apples in the world. The more reasonable assumption is that he will eat at most those three apples.

Of course he could eat one, or two, or all three of the apples. The exact number is unspecified, and unimportant. The point is that he is eating apples, and not something else.

Outside the window, I see birds flying. (It doesn't matter how many birds, just that there are birds)

My mother bought me shoes for my birthday (It could be one pair, or multiple pairs of shoes. Which is not important, the point is that I was given shoes)

This room is where they store computers before they sent to the customer (The number of computers is not important, only that this room is used for their storage).