Trigger housing is aluminum or plastic, pins are steel. If you peen or stake the ends of the pins you run more chance of wallowing out their holes when / if you drive them out again.
Assuming an aluminum trigger housing what I would do is degrease the pins and pin holes. A little rubbing alchohol on a q tip would be fine. Assemble everything and hit the outboard ends of your pins with a dab of loctite blue or clear finger nail polish. Don't need much, just enough to hold. You want just a dab to wick between the ends of the pins and the housing but not so much to run down the pins inside the housing.
Now if your housing is plastic, I would use just plain Elmers white school type glue. It won't be very permanent, but it should give the pin enough resistance on each end to stay in place.