You are close. In that kind of sentences, the adverb déjà is normally located between the verb and the past participle so the correct form (if any) is:

Il le lui y a déjà envoyé.

That’s a lot of pronouns though, so you would hear instead:

Il le lui a déjà envoyé.

or simply:

Il lui a déjà envoyé.

If there need to be specified, là-bas might be used instead of y:

Il le lui a déjà envoyé là-bas.

or

Il lui a déjà envoyé là-bas.

Negative is built using ne pas with ne immediately following the subject and pas after the verb, e.g.:

Il ne lui a pas déjà envoyé.

Il le lui y a déjà envoyé.

And for the negative form, déjà become encore.

Il ne le lui y a pas encore envoyé.

Good reference for pronoun order.

But i think both sentence are just for academic purpose. It’s not really easy to understand sentence like that.