If the activity is still taking place, or the state or condition still holds, at the time reached, then it will be appropriate to use 'have been [doing something]' . . for [a period of time]/since [a point in time, or an event].

The simple form  'we will have [done something]'  refers to a situation which will have ended by the time reached, but is also used even when this is not the case.

'We will have moved home by Christmas'

'He will have returned from his trip by then'

https://en.wikipedia.org/wiki/Uses_of_English_verb_forms#Future_perfect_progressive

Gives the following examle:

"He will be very tired because he will have been working all morning."

Он будет очень усталым, т.к. проработает всё утро.
"By 6 o'clock we will have been drinking for ten hours."
К 6-ти мы уже будем десять часов пить.

And
"I shall have finished my essay by Thursday."
"When I finally search him he will have disposed of the evidence."
"By next year we will have lived in this house for half a century."

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Now me question to native speakers:
Why
"By 6 o'clock we will have been drinking for ten hours."
But:
"By next year we will have lived in this house for half a century."
???

Why not 'have been living'? Semanics is very similar: some process was going on for some time.

Может буквально? I will have done [it].
"я буду иметь это сделанным".
Т.е. к тому момент дело уже будет сделано, причем мной.

I will have been doing
"я буду иметь [себя] бывшим делающим" =
"я буду иметь себя делавшим".
Т.е. к тому моменту я уже успею этим позаниматься (дело, возможно, еще не сделано, но опыт появился).

Что-то на ум приходят неприличные варианты:/ Ладно.

OK, how would you understand the difference between past perfect simple and past perfect continuous? :)  It works the same way, simply shifted into the future.

THANKS A LOT)) can  u please give some examples to me