The verb »gelingen« can be translated into english, but not in the same grammatical context. I show you what I mean:
The standard usage of »gelingen« is:
Etwas(Subjekt) gelingt(Prädikat) jemandem(Dativobjekt).
In english you use the word »succeed« to translate »gelingen«, but it needs a different grammatical environment.
Somebody(subject) succeeds(predicate) in(preposition) something(object).
So in english you say:
(if more than one word builds one grammatical unit, then I put this group of words in brackets.)
(The painter)(subject) succeeds(predicate) in(preposition) (his painting)(object).
But German »gelingen« would need this structure:
(The picture)(subject) gelingt/succeeds(Prädikat/predicate) (the painter)(object).
You see the big difference: Now the picture is the subject, and so the picture is the part that is doing something. It gelingt. And the Object tells us to whom the picture gelingt. It is the lucky painter who receives the pictures gift.
So in German you say:
(Das Bild)(Subjekt) gelingt(Prädikat) (dem Maler)(Dativobjekt).
Or (same pattern):
Alles(Subjekt) gelingt(Prädikat) (unserem Sohn Jan)(Dativobjekt).
And now comes a very valuable feature of German language:
Flexible word order
German word order is much more flexible than English word order. In German we have cases which force nouns to have different endings and other articles. So we know from this grammatical induced variations which syntactic function with part of a sentence has, even if the word order did change. And we often use this feature to put those parts, that we want to emphasize, at the beginning of a sentence.
Changing the order of parts of speech is not completely free (most important: Predicate must stay at position 2), but to swap subject and object is almost always allowed. So you can also write:
(Unserem Sohn Jan)(Dativobjekt) gelingt(Prädikat) alles(Subjekt).
Well, this was it for sentence 1.
Now let's analyze sentence 2:
»Ihn« is a personal pronoun. And as every pronoun it is a placeholder for something else; in this case for our son Jan.
But even if a pronoun refers to something outside its own sentence, it has the follow the grammatical rules of its own sentence. So it does not matter if our son Jan is used in his own sentence as Subjekt, as Dativobjekt, as Genitivobjekt or in what case ever. The case of the pronoun has to follow the rules of its own sentence.
So let's have a look at this sentence:
The predicate of this sentence is:
aufregen (engl: to upset)
It can be used in two ways:
Jemand/etwas regt jemanden auf.
Jemand/etwas(Subjekt) regt(Prädikat; erster Teil des trennbaren Verbs) jemanden(Akkusativobjekt, transitiv) auf(Prädikat; zweiter Teil des trennbaren Verbs).
Jemand regt sich auf.
Jemand(Subjekt) regt(Prädikat; erster Teil des trennbaren Verbs) sich(Akkusativobjekt; reflexiv) auf(Prädikat; zweiter Teil des trennbaren Verbs).
Das Verbrechen regt die Bürger auf.
The crime upsets the citizens.
Note, that here the crime is doing something, and the citizens are the target of the crimes doing. The traget is different from that part that is active. This is what transitiv means. The crime transforms the citizens. It makes them excited.
Die Bürger regen sich auf.
The citizens get upset.
In the German sentence the citizens are doing something, and what they do influences themselves. This is what reflexiv means.
The english translation follows a different grammatical pattern. Note, that in the English sentence the word upset is not a verb but an adjective. The verb (and predicate) is get.
Using the first pattern (transitiv) you can build this sentence:
Fast nichts regt ihn auf.
Almost nothing upsets him.
With grammatical functions:
(Fast nichts)(Subjekt) regt(Prädikat 1) ihn(Akkusativobjekt) auf(Prädikat 2).
So here you find the word »ihn«. It refers to a male person somewhere outside this sentence, and is stands in accusative case, because the predicate aufregen forces its object to be in that case.
word order, again
But to the speaker obviously it is more important to tell us who gets excited (him) than what is the reason for his excitement (almost nothing). So the speaker puts him at the beginning of the sentence. The first part of the predicate must stay at position 2, and the second part at the end, so the subject can move between the two parts of the predicate, where the object was before:
Ihn(Akkusativobjekt) regt(Prädikat 1) (fast nichts)(Subjekt) auf(Prädikat 2).