Yes, 5 hours should be enough - as long as weather or mechanical problems don't significantly delay your incoming flight.

If you need to arrive at EWR 2 hours early - IMHO cutting it close when you have to get boarding pass and check in - and you allow 1.5 hours for JFK to EWR and 45 minutes from wheels down to the street at JFK - then you actually have 45 minutes as a cushion.

I wouldn;t do this transfer at all - but 5 hours should be safe.