I would contact one of our on-board pipers, such as JS Sanders in Memphis or Piobear in Florida for their opinion on appropriate protocol.
In case anyone else is interested in my opinion on such matters...

"An aerial balloon release; that's a new one on me. I'd model it after a burial at sea (which I'm much more familiar with), which in regards to protocol is really not too different than an inurnment or graveside service (unless military). Typically, there is a committal ceremony, then the cremains are ceremonially dropped overboard.

It should be a no-brainer, but sadly it's not. At the very beginning, tell (don't ask) everyone to turn their cell phones, pagers, Blackberries, what-have-you OFF!

DO NOT SET YOUR CAR ALARM! Nobody's going to mess with your car, and a cat jumping on your hood to warm himself won't disrupt the service and spoil the moment.

If the ceremony takes place on turf (unpaved); ladies would be well advised not to wear heels, at least around here.

Generally speaking, "paying the piper"; ceremonially presenting them with a dram, with which they give a formal toast, toss it back, then flip the quaich over and kiss the bottom, is done at formal dinners, wedding receptions, etc., although it's been known to happen informally at wakes and receptions after funerals, too... a standard-issue whisky glass will suffice (a shot glass is much too small for a friendly dram, unless your piper really sucked!).

If there is a memorial service prior to the balloon release, eulogies are usually rendered there (unless in conflict with religious strictures); if not, they can be incorporated into the memorial service at the release site.
If there was no memorial service prior to the release, in addition to eulogies I would suggest the display of photos and mementos of your parents be incorporated; while photo boards are wonderful displays, bear in mind the possible wind and weather conditions as you'll be outdoors, and plan accordingly. The same holds true of things like candles; they can be used outdoors, but not without some planning.

I would suggest piping a prelude, which calls everyone's attention to the task at hand, and marks the beginning of the ceremony. This may be a lament or funeral march specific to the decedent's associations in life. There is often a hymn at the end of the interment service; typically "Amazing Grace", but there are many lovely laments and slow airs which might be appropriate. If burial at sea, or attending the actual interment, and in your case, watching the balloons floating away, I would suggest piping something appropriate at that moment. With burials at sea, particularly for naval personnel, I often "pipe the side" on a boatswain's pipe as the cremains are dropped overboard.
Particularly at graveside or inurnment services, after the family, officiant, or funeral director thanks the guests for their support of the family, announces a reception to follow, etc, I pipe a retreat march of some sort to mark the close of the ceremony.

Keep in mind that if either of your parents were veterans and it hasn't been incorporated into any previous memorial, they are entitled to military honors, which at the minimum includes a flag, a two person honor guard (one of which must be from their branch of service), a flag, and "Taps". Military honors are typically rendered at the conclusion of the service. In this case, the flag would be ceremonially unfolded, "Taps" sounded, and the flag folded into the traditional "cocked hat", and ceremoniously presented to the next of kin. A little known bit of protocol here; If you're a civilian, at the sounding of "Taps", place your hand over your heart.
When carrying cremains of a veteran, someone else carries their folded flag too, which is typically displayed during the service alongside the urn upright, on a tabletop picture frame stand, or in it's formal wood-and-glass triangular display case. If you're a civilian, as the flag-draped casket or flag and cremains passes in front of you, place your hand over your heart.

I do my very best to tailor my performance to the family's needs; the decedent's interests, faith, branch of service, and/or heritage determine the selection of tunes I would suggest. Your piper should do the same."