Convert active to passive

I in comments wrote to John Lawler:

What, you don’t like “The stu­dents will go down­town for lunch” be­com­ing “Down­town will be gone to by the stu­dents for lunch” much, eh? :-) Be­cause such abom­i­na­tions do crop up from not-na­tive speak­ers from time to time, I sus­pect no­body ever let them in on the joke in the first place.

And then to the asker:

You can't ever do pas­sive in­ver­sion on in­tran­si­tive verbs, in­clud­ing both yours and mine. If what I wrote sounds right to you, some­body has trained you wrong be­cause it’s com­pletely un­gram­mat­i­cal in English. You must have a ­tran­si­tive verb with a di­rect ob­ject to use pas­sive in­ver­sion on so that you can in­vert sub­ject and ob­ject. In­tran­si­tive verbs lack an ob­ject to use for the sub­ject.

Also, home­work is a mass noun not a count noun, so you can never say *a home­work.

You are correct,

The hall will be assembled by the students.

indicates that the students are building or constructing the hall in some way.

Your second suggestion,

The hall will be assembled in by the students.

is technically correct but sounds quite strange to me. I'm not sure what you need this for, but you might consider substituting a synonym for "assembled." It might sound more natural as something like

The hall will be filled by the students.

The hall will be the location of the student assembly.

According to Merriam-Webster's Dictionary: assemble  transitive verb to bring together (as in a particular place or for a particular purpose) They assembled a team of experts to solve the problem. So, the passive sentence is: 'The students will be assembled in the hall.' As about the logical subject, it is omitted here.