What are the rules about two verbs in active/passive conversion?

There are many types in this I suppose. Like two clauses , or verbs with prepositions etc. e.g - Smoke and flames engulfed the area and made rescue operations difficult.

What will be it's passive voice ?

Solution 1:

I'm going to change made difficult into the more obviously active verb hampered.

Smoke and flames engulfed the area and hampered rescue operations.

Here, your two active verbs can each be passivised, retaining their respective agents and patients.

The area was engulfed by smoke and flames.
Rescue operations were hampered by smoke and flames.

If you want to retain both passive forms, then the agent smoke and flames needs to come at the end but you still need two patients:

The area was engulfed by, and rescue operations were hampered by, smoke and flames.
The area was engulfed, and rescue operations were hampered, by smoke and flames.

That is very awkward. The usual form is to retain an active verb in a relative clause:

The area was engulfed by smoke and flames, which hampered rescue operations.
Rescue operations were hampered by [the] smoke and flames which engulfed the area.

Note the comma! The British Council has notes on relative clauses, which can be applied to these sentences:

1. We use relative clauses to make clear which person or thing we are talking about:

   Rescue operations were hampered by [the] smoke and flames which engulfed the area.

2. We also use relative clauses to give more information about a person, thing or situation:

   The area was engulfed by smoke and flames, which hampered rescue operations.