What are the strengths and weaknesses of Lepidus and Cassius in Julius Caesar?

In Shakespeare's Julius Caesar, it is ironic that in Act
I Cassius tells Brutus

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Men at some time are masters of their
fates:

The fault, dear Brutus, is not in our
stars,

But in ourselves, that we are underlings.
(1.2.145-147)

For, Cassius is
at times master of his fate, and at others is himself superstitious and
weak. 

In Act I, Scene 2, from which these lines come
Cassius persuasively convinces Brutus to join the conspiracy to assassinate Caesar.  In
Act III after the men have slain Caesar, it is Cassius who recognizes the threat that
Marc Antony poses; he advises Brutus to have Antony killed.  But, Brutus tells him that
they will make a friend of Antony.  Wisely, Cassius replies that his doubts always turn
out to be justified,

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I wish we may.  But yet have I a
mind

That fears him much; and my misgiving
still

Falls shrewdly to the purpose.
(3.1.158-160)

Then, when
Brutus gives Antony permission to address the Romans after he does, Cassius warns him
against doing so:  "You know not what you do" (3.1.250),  His suspicions of Antony are
correct, but he defers to Brutus.  Still, he expresses his
anxiety, 

I
know not what may fall; I like it not he defers to Brutus.
(3.1.262)

Of course, Marc
Antony turns against them and becomes their mortal enemy, fomenting a civil war, and
defeating them at Philippi.  Even there, Cassius's assessments are correct, for he
suggests that his and Brutus's troops to remain at Sardis and force the others to
advance so that they will be fatugued and use valuable resources, but Brutus disagrees. 
As it turns out, Cassius again is correct, although he has acquiesced to
Brutus.

But, just before this final battle, Brutus and
Cassius quarrel bitterly.  Cassius accuses Brutus of wronging him repeatedly, and
complains weakly that Brutus no longer loves him:

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Hath Cassius
lived

To be but mirth and laghter to his
Brutus

When grief and blood ill-tempered vexeth him?
(4.3.124-126)

just as he has
been worried in the first act: 

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Brutus, I do observe you now of
late;

I have not from your eyes that
gentleness

And show of love as I was wont to have
(1.2.36-38)

Finally, Cassius
becomes weakly superstitious.  In Act 5 he talks to Messala, telling him that even
though he "held Epicurus strong" and has not believed in omens, now he has
seen

Two
mighty eagles fell, and there they perched,

Gorging and
feeding from our soldiers' hands,

Who to Philippi here
consorted us.

This morning are they fled away and
gone,

And in their steads do ravens, crows, and
kites

Fly o'er our heads and
downward....

Our army lies, ready to give up the ghost.
(5.1.87-93)

In the end,
Cassius still has wisdom, but he is fearful and superstitious, and defers to
Brutus. 

________________

One
of the triumvirs after the death of Caesar, Lepidus is considered unworthy to be one of
the three rulers of the Roman empire by Marc Antony, while, on the other hand, Octavius
is willing to honor him as "a tried and valiant soldier" (4.1.32).   At the beginning of
Act IV, the triumvirate compile a death list of their political enemies.   Lepidus is
sent to get Caesar's will so they can reduce some of the legacies in it; when he
returns, with a lack of honor, Lepidus  consents to allow his brother to die provided
Antony will sacrifice his nephew.  So, while he may be an excellent soldier, Lepidus
lacks loyalty to his family.