How to pronounce "two boys' families"?
"two boyses family" or
"two boys families"?
Generally (i.e. "properly"), option 2. As a general rule, the apostrophe is silent.
That said, there may be situations where a native speaker would use pronunciation #1. For example, they may speak a dialect in which it is pronounced as "boyses", or they may be deliberately mispronouncing it for emphasis (for example, my family sometimes does this), especially if there were emphasizing a plurality of boys, as "boys" sounds identical to "boy's".