"Placing unrealistic, demanding, and very-hard-to-fulfil expectations on children can negatively impact on their mental well-being."

[hardyweineberg]

"Placing unrealistic, demanding, and very-hard-to-fulfil expectations on children can negatively impact on their mental well-being."
Source: me

Is the phrase very-hard-to-fulfil grammatical, correct, and acceptable? I have no idea whether this is allowed in English.

 

[Barque]

It's informal but acceptable. The writer's using a four-word phrase as an adjective.

 

[jutfrank]

Whether it's acceptable depends on the register of the text it's intended for.

It's quite obvious what you're trying to do and why but I don't like it. There's no need to turn a perfectly normal adjective phrase into what is in my judgement an inelegant and ungainly compound. I think the sentence reads just as well without the hyphenation.