I strongly recommend a Velcro strap to prevent the front wheel from either rotating or turning (much) side to side. That, one solid object, and careful process, cover a lot.
My procedure as family lead stoker on our double-double was:
Stop short of a tree or pole that was solid.
Walk forward, precisely aligned for small tilt, right next to the pole at my seat position.
Tell the 5-year old to climb down from the kid back stoker of the tandem.
Securely Velcro the fron wheel to the downtube.
Swing leg off the tandem. Lean it gently against the pole or tree.
Walk hands along the bike back to the tandem-trail-a-bike, front seat. Unbuckle the seat-back strap holding the 3-year old, lift her into the ground.
Walk hands back the the child seat on seatpost mount. Unbuckle and lift down the 1 year old.
Walk to front of bike, unhook panniers with diaper bag, picnic blanket, lunch, and IPA.
Feed kids, drink IPA as they play in the park.
Reverse above.
Ride home 10 miles.
Survived another Saturday.