Can adjectives be used like this? (genitive)

It's easier to explain myself with examples like:

The dead's last wish was... The long-lost's children were found (if long-lost refers to, for example, their long-lost ancestors, or basically anybody else depending on the context) The cursed's sword was buried with him, etc.

It seems as if in these sentences (if they were correct) the adjectives turned into "nouns".

I believe these examples would be correct like this for sure:

The last wish of the dead was... The children of the long-lost (parents?) were found, The sword of the cursed (warrior) was buried with him, etc.

My question is whether it was possible to use adjectives and genitives together? Or can it depend on the context? I'm Hungarian, and in Hungarian we can use adjectives like this, since they become instantly nouns, and any adjective can be turned into a noun like this. I'm just not sure whether it was also the case in English or not. I've seen such stuctures in books, movies and video games, but I'm unsure if those were only "literary exceptions" or they were also grammatically correct.

Thanks for your help!

Yes, in general, those are acceptable. Whether they are a good choice from the point of view of clarity and style will depend on the context and the writing skills of the author. They are not particularly rare, but they are also not particularly common, in the sense that it is quite likely that you may go through several newspaper articles without encountering any.

Discussion

According to CGEL, when the dead, the long lost, etc. are used as a noun phrase (NP), that type of NP is called a fused modifier-head. There are various types of fused modifier-head NPs. Here we are talking about a type that we might call the 'adjectival type', i.e. the type that consists of a definite article and an adjective, plus possibly a modifier in between. The only general constraint on the type of adjective allowed is that it must be possible to use the adjective attributively (CGEL, p. 529).

CGEL doesn't explicitly comment on the genitive form of these adjectival fused modifier-head NPs. But it is not uncommon to see them in the genitive.

Here are some examples of usage. First, from the Corpus of Contemporary American English (COCA):

Police said two more bodies were found in one of the dead's apartments.
…which limits the poor's access to the market…
…can't be brought up if their only purpose is to provide evidence of the accused's character.
…paid time off for mothers and fathers at any time during the newborn's first six months.
…the mother wrapped her forearm around the eldest's neck.

And from the British National Corpus (BNC):

It was found in a cardboard folder in the back of the accused's car.
It is not because of the poor's isolation from the modern sector that they remain poor.
…with the provincial's enthusiasm for champagne…
…flowing from the insured's death.
He was opposed, to shinty and the young's enjoyment in general.

The phrase the long lost's doesn't occur in these corpora, but it does occur e.g. here:

Occurrences beyond human control such as a chance meeting, a hurricane, the long lost's appropriate return, if they come early in the story and are apparently of no great consequence to the plot, have no effect on plausibility.
^{From Kenneth Payson Kempton, The Short Story (1954) (link)}