Wild, Fische, und selbst die Tiere in den Staellen erfroren
In this sentence,
The whole subject is: "Wild, Fische, und selbst die Tiere.."
This can be further decomposed into "Wild, Fische, und selbst die Tiere" and "in den Stallen". I identify "in den Stallen" as a prepositional object, but then, what is "Wild, Fische, und selbst die Tiere" supposed to be?
The predicate of your sentence is "erfroren", and the subject is "Wild, Fische, und selbst die Tiere in den Staellen". The subject is an enumeration in three parts: "1. Wild, 2. Fische, 3. selbst die Tiere in den Ställen." Here, "in den Ställen" is an attribute / a modifier to "Tiere" (it says where the animals are). The fish obviously won't be found in a stable, so the "in" must belong more narrowly only to "Tiere".
"In den Ställen" is not called a prepositional object here (which would mean: object of a verb).
The whole subject is: "Wild, Fische, und selbst die Tiere.."
No - and this seems to be the root of your problem. German (and this has often been said) is a V2-language. That means the Prädikat (the inflected part of the Verb) goes to second position. (Note, this is true for Hauptsätze, main sentences, not Relativsätze, relative sentences or Imperativsätze, commands.)
This also means that everything going before the Verb is first position (there is something called Vorfeld, but I keep it simple here) - which, in this case, is the Subjekt of the sentence.
A Subjekt is, in its most basic form, a Nomen (noun).
Der Schirm fehlt. (The umbrella is missing.)
But there can be all sorts of additional parts to the Subjekt as long as they are related to the Nomen establishing it. Attributes (Adjektive or even whole phrases):
Der rote Schirm fehlt. (The red umbrella is missing.)
Der von mir in der Garderobe vergessene Schirm fehlt. (The umbrella left by me in the wardrobe is missing.)
But also lists:
Der Schirm, der Stock und der Hut fehlen. (The umbrella, the walking stick and the hat are missing.)
And, on top, all these can be combined: lists, consisting of elements which have attributes along with them (which themselves could be lists ...):
Der rote Schirm, der Stock mit dem Silberknauf und der Hut mit dem großen goldenen Abzeichen fehlen.
Here we have a Subjekt consisting of a whole phrase (it is fittingly called a Nominalphrase):
Der rote Schirm, der Stock mit dem Silberknauf und der Hut mit dem großen goldenen Abzeichen
The Subjekt consists of a list with three elements:
Schirm
Stock
Hut
The first element consists of the Nomen along with an attribute defining it more narrowly, the Adjektiv "rot".
The second element is basically the same, but here the attribute is not an Adjektiv but a phrase itself: "mit dem Silberknauf" (with the silver knob).
The third element is also a Nomen with an attribute but in this case the attribute is a phrase itself ("mit dem ... Abzeichen") with a list of attributes ("großen goldenen") in it.
You can add layer upon layer because these structures are recursive. It has been done and it is perfectly possible to overdo it - still grammatically correct but considered bad style.
At last, coming back to your original sentence which you should be able to parse yourself now:
Your Prädikat is "erfroren", which is Plural, dritte Person, Präteritum, Aktiv - "They froze (to death)." You have a subject consisting of a list (which is why the Verb is in Plural):
Wild
Fische
Tiere
The first two elements are simple, the last one has an attribute along with it, consisting of a phrase:
Tiere in den Ställen
Don't be confused by the "selbst", it simply means "even" and just emphasizes. The structure is the same as in English:
The game, the fish and even the cattle in the stables froze to death.
