Which lines in act 4, scene 2, support this metaphor: "For the poor wren, the most diminutive of birds, will fight, her young ones in her nest, against the owl." I need eight examples.

The line is spoken by Lady Macduff in act 4, scene 2, after she hears the terrible news that her husband has taken off for England in fear for his life, leaving his family at the mercy of Macbeth. Lady Macduff is absolutely scathing at what she sees as her husband's cowardice. Even a tiny mother wren in her nest will defend her chicks from a big owl, she says, yet Macduff has run away at the first sign of trouble, despite being quite evenly matched with Macbeth.
Macduff's son shames him by telling his mother that he will live the way birds do. Not by eating worms and flies, as his mother thinks, but by living on whatever he can find. Lady Macduff is not quite so sure; her son would not be much good as a bird. For one thing, he does not know enough to watch out for potential traps. To this, her son gives the spirited reply:

Why should I, mother? Poor birds they are not set for. My father is not dead, for all your saying.

Under the circumstances, Macduff's son is showing remarkable fortitude, but, then again, he still does not accept that his father is a traitor. He also does not see why on earth he should present such a threat to anyone. In his youth and innocence, the boy is showing the kind of raw courage of which his father was incapable. If a big old hungry owl should ever descend upon his nest, we can be sure that he will fight as hard as his mother wren.
But the mother wren herself, Lady Macduff, is already doing an admirable job of protecting her son; she does this not by feeding him comforting lies about his father, but by telling him the truth as she sees it. The truth, according to her, is that Macduff is a traitor. As far as she is concerned, he might as well be dead. She is certainly dead to him, if not to her son:

Sirrah, your father’s dead.

The whole, unvarnished truth is an essential part of Lady Macduff's strategy to protect her son from the dangers ahead. The definition of a traitor might be a little abstract for a child, so Lady Macduff breaks it down to make it easier to understand:

Why, one that swears and lies.

It is understandable at this point that Lady Macduff is not thinking about acquiring a new husband. Whatever happens, she now seems resolved on defending her children, with or without a husband. Husbands are easy to find anyways:

Why, I can buy me twenty at any market.

The mother wren will raise her brood alone, if needs be.
Lady Macduff seems resolved to protect her son. She instructs him in important lessons of statecraft, such as what should happen to traitors, to those who lie and break their promises:

Every one that does so is a traitor and must be hanged.

Suddenly, a messenger arrives, bringing with him bad tidings. It is now that the metaphor of the diminutive mother wren really comes into its own. The messenger tells Lady Macduff that she and her children are in serious danger and must leave at once. But Lady Macduff is defiant. Having castigated her own husband for running away to save his own skin, she is not about to do likewise; she will not fly the nest:

Whither should I fly? I have done no harm. But I remember now I am in this earthly world, where to do harm Is often laudable, to do good sometime Accounted dangerous folly. Why then, alas, Do I put up that womanly defense, To say I have done no harm?

Macbeth's hired killers then enter, hellbent on wiping out Macduff's family. However, Lady Macduff, this "diminutive wren." is defiant, still displaying extraordinary courage in the face of her imminent, violent death. When asked about the whereabouts of her husband, she replies to the murderous thug with utter contempt:

I hope, in no place so unsanctified Where such as thou mayst find him.

The implication here is that the killers are so evil that they are used to spending time in places which are "unsanctified," that is to say not holy.
It is not just Lady Macduff who shows bravery in her last moments on earth; her son also demonstrates remarkable courage. The first murderer calls Macduff a traitor, which ironically is exactly what Lady Macduff called him a few moments before. But Macduff's son is not going to stand for that:

Thou liest, thou shag-haired villain!

For this valiant insult, Macduff's son is brutally stabbed to death. Yet just before he expires, he begs his mother to run away. Unlike Macduff's undignified departure, this would not be an expression of cowardice, but of absolute necessity. Lady Macduff runs off, screaming murder. The mother wren did her very best to protect her brood, but with the death of her son, there is nothing more that can be done. She has no choice but to fly.