Welcome Obi-wan
Nicomachean Ethics and Magna Moralia
These need to be peeled apart since they have unequal claims to have been written by Aristotle. While the Nicomachean Ethics is widley regarded as the work of Aristotle, the balance of scholarly opinion is that the 'Great Ethics' or Magna Moralia is post-Aristotelian. The bases of doubt are numerous, namely:
... matters of language and style in
which the Magna Moralia seems to diverge sharply from the
admittedly genuine works; (2) a few personal and other references allegedly pointing toward a post-Aristotelian date; (3)
supposed Stoic influences in terminology and doctrine; (4) a
general impression, very strong in a few relatively isolated passages, that the author of the Magna Moralia wrote with the
Eudemian and Nicomachean Ethics open before him, excerpting,
condensing and abbreviating so as to produce a kind of hand-
book of Aristotelian moral theory. (John M. Cooper, 'The Magna Moralia and Aristotle's Moral Philosophy', The American Journal of Philology, Vol. 94, No. 4 (Winter, 1973), pp. 327-349: 330.)
Yet the Magna Moralia is a useful source book for Aristotelian Ethics:
First, on some
issues the simpler treatment found in the Magna Moralia
presents more adequately a basic insight which the other, more
elaborate treatments tend to obscure; these insights can be
claimed for Aristotle, if the treatise is genuine, and used to bring
into clearer focus the theories of the other ethical writings.
Secondly, in several instances the Magna Moralia includes dis-
cussions of important and difficult points never explicitly faced
in the other treatises: the most noteworthy instance of this is
the discussion of the question what to do in case the rules of two
virtues dictate conflicting actions in a particular situation (Mag.
Mor. 2.3.1199 b 36-1200 a 11). Thirdly, where the Magna
Moralia differs in doctrine from either of the other treatises the
exact determination of the differences, if they can be presumed
to be due to Aristotle himself, always throws interesting new
light on the theories and arguments of the other version. Thus
the Magna Mloralia (1.33.1193 b 24-30) explains justice as a
mean between getting more and getting less than one's share. the treatise is genuine then its account of justice both serves to
explain the occasional half-survival of the same view in Eudem-
ian Ethics 4 (= Nicomachean 5) and to point up the nature
and degree of Aristotle's later achievement in getting beyond
such a restricted understanding of justice (on this see further
below, section 2). Again, the fact that the Magna Moralia con-
sistently, clearly and repeatedly (1184 a 29-38, b 33-39 with
1204 a 26-29, 1185 a 25-26, 36-39, 1208 b 3-6) maintains a
unified conception of evdatLovta as consisting, without discrimina-
tion, of the exercise of both the moral and the intellectual virtues,
cannot but throw important new light on the related theories of
the Nicomachean and Eudemian Ethics.
In all these ways then, as well perhaps as others, the Magna
Moralia is a very important document for scholars and philoso-
phers interested in understanding Aristotle's moral philosophy. (Cooper: 328-9.)
I have dwelt on the Magna Moralia because you clearly regard it among 'his two other works on ethics' alongside the Nicomachean Ethics. It isn't among his 'two other works' - at least such is the majority view among scholars.
Nicomachean and Eudemian Ethics
If you have read the Nicomachean Ethics you have already read a portion of the Eudemian Ethics since Eudemian Ethics books 4-6 are the same as Nicomachean Ethics books
5-7. These are the 'common books'. By all means tackle the Eudemian Ethics but expect a bumpier ride. For all that translators can do to help:
The Greek text is not only riddled with
corruption, obscure expression, and puzzling grammar, but even where
the diction and syntax are clear, the arguments are often dense and
cryptic. Previous scholars have not done enough to illuminate this
difficult text. They give little insight into the more opaque arguments
and how they contribute to broader lines of reasoning. Sometimes they
make these shortcomings even worse by failing to offer a translation of
the common books, leaving readers with an incomplete text and little
guidance in understanding Aristotle's expressed views and how they
might fit together into a considered philosophical ethics. (Carlo DaVia, 'Reviewed Work(s): The Eudemian Ethics of Aristotle. Translation and Commentary by
Peter L.P. Simpson', The Review of Metaphysics, Vol. 67, No. 3 (MARCH 2014), pp. 668-670: 669.)
We don't know why common books keep company with differences of text in the other books of the Nicomachean and Eudemian Ethics. Some argue that the two Ethics have different dates of composition, justifying common books where Aristotle had not changed his mind but requiring different texts where he had. If the two works represent different stages in Aristotle's philosophical development, the case is not clear. The possibility shouldn't be overlooked that the two books were contemporary and that aside from the common books Aristotle used one text or the other, depending on his intended readership. Hence it may be that:
the Nicomachean Ethics and Eudemian Ethics
differ because the former served as a vademecum for legislators,
whereas the latter served as an apologia pro vita sua for fellow
philosophers. (DaVia: 669.)
Anyhow, the two works are not identical and you can usefully explore their differences, of which the following gives a foretaste:
One example [of difference: GLT] which calls
for further attention is Aristotle's Eudemian claim that
there are just three types of orexeis (EE 1223a27-28)
which leads him to regard reason and inclination as
distinct motives for voluntary action (EE I225a27-28)
and to treat proairesis, on occasion, as distinct from orexis
(EE 1223a26-8; 1225b25). This view appears to motivate a separate diagnosis of acrasia and self-control (EE 1224a24-25, b22-24) as a conflict between reason and
orexis, and a more intellectualist picture of the virtues
(esp. EE 1229a1-2, b22-24, 1232a35-8 in Book III ... Thus Aristotle's Eudemian characterisation of
virtue as requiring one 'to be as far as possible
unconscious of the irrational part of the soul' (EE
1249bi15-25) appears to result from a different psychological theory from that which takes virtue to require a
modification and subtilization of lower-level desires
(NE II02b29-34, 1119bI4-18, NE/EE 1144a7ff.,
1151a16-18. (David Charles, 'Reviewed Work(s): Eudemian Ethics. Books i, ii and viii. by Aristotle and M. Woods', The Journal of Hellenic Studies, Vol. 107 (1987), pp. 203-204: 203-4.)
