I hate to be the lone dissenting decision, but you should absolutely get alpacas. From your list - bagpipes, cello, piano, alpaca - which is going to stick in people's heads the most, making it a truly memorable day? Alpacas, every time.
If you're worried they'll upstage the other entertainment, I'd say a reasonable compromise would be to keep them up your sleeve (so to speak) until the ceremony itself to give the musicians their due, then let the ring-bearers loose with a big entrance.
Show-stealing? Yes. Memorable? Oh, yes. Is that a bad thing? Not in my book...