Post contionem cives inter se disputant utrum decretum bonum sit.

Because post is a preposition that takes the accusative in Latin. So post contionem means after the meeting / after the speech.

Here:

• post = after
• contionem = accusative singular of contio

So this is not the direct object of a verb; it is simply the object of the preposition post.

Cives is the subject of disputant.

• cives = citizens
• it is nominative plural
• disputant = they discuss / argue / debate

So cives disputant means the citizens discuss.

Inter se means among themselves or with one another.

This expression is very common in Latin:

• inter = among, between
• se = themselves

So cives inter se disputant means the citizens are discussing with each other, not just speaking in general.

Because se is the reflexive pronoun. It refers back to the subject of the clause, here cives.

So:

• se = themselves
• eos = them

If you used eos, it would normally refer to some other group, not back to the citizens themselves. Since the idea is the citizens argue among themselves, se is the right pronoun.

Utrum introduces an indirect yes/no question, meaning whether.

So the citizens are debating whether the decree is good.

A useful contrast is:

• direct question: Utrum decretum bonum est? = Is the decree good?
• indirect question: ... disputant utrum decretum bonum sit. = ... they discuss whether the decree is good.

Because Latin normally uses the subjunctive in indirect questions.

The clause utrum decretum bonum sit is an indirect question introduced by utrum, so sit is exactly what we expect.

Compare:

• direct question: decretum bonum est? = is the decree good?
• indirect question: utrum decretum bonum sit = whether the decree is good

Even though sit is subjunctive, in English we usually still translate it simply as is.

Yes. It is a subordinate clause, specifically an indirect question.

Its parts are:

• utrum = whether
• decretum = the decree
• bonum = good
• sit = is

So the whole clause means whether the decree is good.

Decretum is the subject of sit, and bonum is a predicate adjective describing it.

Both are:

• neuter singular
• in the nominative

That agreement is important:

• decretum = decree
• bonum = good

So literally: whether the decree may be good / is good, with bonum agreeing with decretum.

Yes. Utrum often appears by itself to mean simply whether.

Latin can also make the alternatives explicit, for example:

• utrum ... an ... = whether ... or ...
• utrum ... necne = whether ... or not

But when only utrum appears, the or not idea is often just understood from context.

Latin word order is much more flexible than English word order. This sentence is arranged in a very natural Latin way:

• Post contionem = sets the time first
• cives = then the subject
• inter se disputant = the main action
• utrum decretum bonum sit = the content of the discussion

So the sentence flows as:

After the meeting, the citizens discuss among themselves whether the decree is good.

Latin could rearrange some of these words without changing the basic meaning, though the emphasis might shift.

Yes. Latin disputare can mean to discuss, to debate, to argue about, or to examine by argument. It does not always imply an angry quarrel.

So in this sentence, disputant could be understood as:

• they discuss
• they debate
• they argue about

The exact English choice depends on context.

A contio is a public meeting, assembly, or sometimes a public speech delivered to a gathered crowd. In Roman contexts, it often refers to an assembly where people are addressed.

So post contionem could mean:

• after the assembly
• after the public meeting
• after the speech

The exact wording in English depends on the context in which the sentence appears.