"They are the children of God"
a síad clann dé íad

Can somebody explain to me the function of the words "íad" (them) and "síad" (they)

How come they are both needed here? It seems like íad is unncessary...

go raibh maith agat as do chuid ama! (Thank you for your time!)

The answer is that you need to learn Irish consecutively from the beginning. Teach Yourself Irish, chapter 1, followed by chapter 2, etc. You don't dip into Ch21 then Ch2 than back into Ch17, or you will learn nothing.

This is just how the language works. As I've mentioned to you before, you cannot expect Irish (or any other language) to do things the same way as English. The use of both pronominal forms in one utterance may seem redundant to you, but they are required in order for the utterance to be grammatical. A learner of English might equally complain that the verb "do" is redundant in exclamations like "I did not go" or "I don't know", because "I went not" and "I know not" are perfectly sufficient alternatives. Nevertheless, we use the redundant construction more readily than the alternative, which in turn is becoming somewhat archaic. Languages don't always do the same things as each other. That variety is part of the beauty of them.

If you want technical details about the use of pronouns with the copula in constructions like this, by all means we can discuss that here, but you'd do well to follow dj's advice and try to work through a grammar book first. It's important to have a foundation in grammatical concepts and terminology before trying to piece apart constructions in a language you're not familiar with. I say this not to be arrogant, and hopefully it doesn't come across as condescending. I bring it up simply because some of us have replied to your previous threads by getting into grammatical detail, and you've responded to tell us that it went over your head. The same is almost certain to happen again if we get into it here, and in any case, it's not necessary to get bogged down in grammar if your goal is simply to learn the language. But, you'll have to be willing to accept that some aspects of it will not be what you might expect.

Okay yeah, you guys are right, I'm sorry. I just get caught up in little things and think "I'll ask one more little question", lol. My local book store doesn't sell any Irish learning books, so I'll have to order one online.

Thanks for your patience with me!

I would not recommend to go through a grammar book as a beginner, but to use a teaching or selftutoring course.
BTW: Unfortunately, most grammar books don’t explain much. They just say: "So it is, get used to it!"

a síad clann Dé íad

The orthography is not standardised.
I’d guess "a" is the relative particle, "s" in siad is the copula.

In Standard Irish orthography it is:
is iad clann Dé iad = (that) they are the children of God.

There is no difference between a main clause and a copula relative clause in Standard orthography.
(And afaik there is no difference in pronunciation in all dialects and all pre-Standard spellings. "a siad, a s’iad, as iad, is iad" are all pronounced "shee(uh)d")
But, obviously, iad is twice.

Clann Dé = the children of God is definite (the children, not some children). It is definite because Dé is definite.
(You can’t say "some children of God" or "a child of God" in Irish, at least not by using genitive Dé.)

Definiteness/indefiniteness is very important in the grammatical structure.
Definite noun phrases (NP) in copula sentences can not be put directly following "is". It is impossible. And that is why a pronoun has to be inserted, called "sub-predicate",
so "is iad NP ..."

In this case, it is iad, plural, though clann is formally singular, but the subject of he sentence is iad, they, too. You would not say "Is é clann Dé iad". It is always "é ... é", "í ... í" or "iad ... iad"
The last "iad" is actually the subject of the sentence.

Admittedly, all grammar books are not created equally, but any good grammar book will cover the basics; what is the copula, what is a relative clause, what are pronouns, etc. This is the kind of foundation it will be necessary to have if you want to discuss what is going on in Irish by deconstructing phrases and sentences.

As for grammar books vs. teaching/self-learning, pick whichever is easiest for you to learn with. I find that 90% of the content of either is going to be the same as the other anyhow, and so I just lumped them all broadly under the banner of "grammar books" here. Maybe that's careless, but which sort is going to be most useful depends on the individual using the book, so I'm not inclined to draw much distinction or to recommend one over the other. Preferably, get both.

The specific book djwebb suggested in an earlier thread is particularly good in my opinion, and has the added benefit of being freely available online.

In "a síad" (=is iad), the "is" is not relative. This is just how William Daniel's New Testament in AD 1602 spelt "is iad". As Labhrás points out, the pronunciation is "'siad" in any case.