Not sure how to pick a pickup for my violin.

ayer

Think about the whole sound system, not just the pick up. Many piezo-electric pickups don't put out enough voltage to go straight into an amplifier. I use a Fishman, and go into a small single tube pre-amp (originally for a microphone), then to a guitar amp. It works fine for me. Search here on the site for prior pickup discussions and you can find lots of comments about different brands of pickups. It may make your head spin about the subtle differences between pickups.
You could also get a microphone and pre-amp, put the microphone on a stand so its over your violin, and send the pre-amp into your uncle's amp.

Go to a large, good electric guitar store and try out different arrangements. Borrow a pickup if a call to the store says they don't have pickups. Ask if they have your uncle's amp so you can plug into one like you'll use for the wedding. Tell the sales rep your objectives and a rough budget and let them help you try different configurations. Your ears will tell you.