Distribute, apportion

1a is not. Neither is 3b.

I made an error in my original post. Here is the corrected post:

1a "He gave money to them."
1b "They were given money."

2a "He provided money to them."
2b "They were provided money."

3a "He distributed money to them."
3b "They were distributed money."

4a "He apportioned money to them."
4b "They were apportioned money."

So, all the b-s

3b does not work with that verb.

The verbs "give", "provide", "distribute", and "apportion" seem to be in the same class of meaning. Yet for:

"They were ___ money."

only the passive particles of "give", "provide", and "apportion" would work, but not "distribute"?

That's right. The form is not so common. 'Provide' more often appears with 'with', too.