Can you put two PRSAs into a single ARF?

My father did, although not at the same time.

The proceeds of the second AVC were added to the ARF a while after the ARF started.
 
Yes.

When you take your retirement options from any of your PRSAs you can do what you choose with them.

After taking any available tax free lump sum you can use the the remaining funds to set up an ARF, or an Annuity, or take a taxable lump sum, or any combination of these.

You could add all the funds into a single ARF if you choose.