MWH has rightly drawn attention to the fact that you seem to be focusing on first trying to understand the Greek and only then thinking about the translation. This is a major advance and you should feel very pleased with your progress. I dont have much to add but you might find the following helpful.
This passage is adapted from a speech written by Lysias in a prosecution brought against Ergocles, an Athenian general who took part in a naval expedition commanded by Thrasybulus during the Corinthian War (395-387 BC). The expedition was initially successful but had disastrous consequences because it alarmed the Persians and caused them to switch sides from Athens to Sparta. The Persians imposed a Peace on the Athenians and their allies which left Sparta in control. Thrasybulus died during the expedition and later on Ergocles came back to Athens. It seems that Ergocles was accused of embezzlement. "At any rate, Ergocles was convicted and executed, despite his having been one of Thrasybulus’ associates in the democratic counterrevolution of 403. "(Todd p.288 “Lysias (Oratory of Classical Greece)” ).
Lysias" style is usually quite clear but it is rhetoric so he makes a lot of use of antithesis and, as MWH has advised, you have to try to retain that sense of structure in your translation. When faced with a passage like this before translating you might find it helpful to copy or type out the Greek and break down the structure something like this:
ἐγὼ δέ, ὦ ἄνδρες Ἀθηναῖοι, οὐ τὴν αὐτὴν γνώμην ἔχω περὶ ἑκατέρων·
τούτους μέν,
οἳ ἐλευθερίας καὶ τοῦ δικαίου ἐπιθυμοῦντες καὶ τοὺς νόμους
ἰσχύειν [“to be strong,” “to be valid”] βουλόμενοι καὶ τοὺς ἀδικοῦντας
μισοῦντες [“hating”] τῶν ὑμετέρων κινδύνων [“dangers”] μετέσχον, οὐ
πονηροὺς νομίζω εἶναι πολίτας·
ἐκείνων δέ,
οἳ κατελθόντες [“returning to
their homeland from exile”] ἐν δημοκρατίᾳ
τὸ μὲν ὑμέτερον πλῆθος ἀδικοῦσι,
τοὺς δὲ ἰδίους [“personal,” “own”] οἴκους ἐκ τῶν ὑμετέρων μεγάλους ποιοῦσι,
μάλα ἰσχυρῶς δεῖ κατηγορεῖν, ὥσπερ τῶν τριάκοντα.
Use the μέν..δέ pairings to understand how the passage works. You might find it helpful to underline the finite verbs and italicise the supplementary participles.
I think you haven’t quite grasped where "ἐν δημοκρατίᾳ " fits in here. The exiles have returned “under [a] democracy”. As MWH mentions the Spartans supported an oligarchy (the “thirty”) in Athens at the end of the Peloponnesian war and many Athenians went into exile (including Lysias who only just escaped with his life). The complication for the whole speech is that Thrasybulus (and presumably Ergocles) were part of the restoration of democracy and the expulsion of the oligarchy.
As Joel has pointed out “κατελθόντες” is aorist (the gloss only gives the sense not the translation). So its better to write something like “having returned home from exile”.
It is difficult to translate Greek rhetoric into clear English without sacrificing something. Generally speaking rhetoric has a poor press these days. But President Obama has a highly rhetorical turn of phrase and of course Martin Luther King Jr. was a highly effective proponent. It is interesting that for rhetoric in English one turns more to American examples. (Perhaps in the UK the disconnect between the promises of post war Churchillian rhetoric and the lack of delivery on those promises devalued it somewhat. I know that some here disapprove of the intrusion of politics into classical studies but rhetoric is an avowedly political category. Lysias’ prosecution speeches can seem thin to us if you dont take account of the political background or the cultural expectations of the audience.)
I once went to a conference and heard a panel of relatively young speakers giving papers on rhetoric. A very distinguished Senecan scholar lent over to me and said with a wry expression " why is it that the people who study rhetoric are so bad at expressing their ideas?" 
He was more interested in his own joke I think rather than the truth of his rhetorical assertion, although the papers were not that exciting.