This is our third season with our tandem and love it. Our goal this season is to get comfortable with both of us standing while climbing. We can do captain standing while going up short hills (learning not to throw the bike to each side), but have a very hard time with both of us standing. Any hints or suggestions? THANKS!
Practice standing on flat roads first (it's a valuable skill for taking periodic "butt-breaks," even if you never see another hill worth standing for). Shift to a rather large gear and give a verbal signal so you and your stoker can rise more-or-less together. Once you've mastered it on the flats, it'll be easy on a hill: same technique without the upshift. Over the years, the verbal signal may become unnecessary. My stoker can apparently read my body English, and we stand together just fine without discussion or hesitation. Though I do ask her if she'd like a butt-break -- to make certain that she's holding on to the 'bars when I stand up :-)
The way I do this with new stokers is to first stand up and coast, on a gentle uphill, in the biggest gear we've got, the 53 X 11T. Then we start pedaling from an already standing position, at first very slowly, and then faster and faster.
Once we've gotten to where we can use this for a tactical tool to top small rollers, the technique is a little different: you call the stand one crank revolution ahead of time, and next time that crank (always the same one) comes around to the 2:00 position, we both stand up at once. Because standing cadence is lower than sitting cadence, I usually upshift two gears on a tight cassette (11-21, 12-21, 11-23).
People try so hard not to disturb each other on a tandem that the normal routine of standing on a single is disrupted, and you do have to make a practice of standing regularly to avoid saddlesores, chafing, numbness, etc.
You may never get good at standing if the stoker does not have room to move forward when standing. I had one stoker (5'11") who just couldn't do it until I moved from the pre-'98 Cannondale J/L with 30" BB spacing to the Meridian with 37" BB spacing. First test ride, first time we stood up, the tandem went straight without the usual bicep-bulging effort on my part. She'd never known before that all she lacked to do it right was the space, but THEN she knew.
Seeing that you can do captain standing only for now, the next step is stoker standing only.
Use loud voice command like "UP! or "STANDING" to indicate both of you will now stand. Yes, do try it on flat terrain first,and don't 'rock' on the pedals as you would on your single, hold upper body still!
We pedal 90 degrees out-of-phase and cannot stand simultaneously; we seldom stand anyway, except in an emergency; either stoker or pilot voices: Standing or up.
We have seen exactly one couple in our 29+ years as a duo that could stand simultaneously while 90 degrees out-of-phase. Looked like a circus act, but do-able!
As for butt brakes, either pilot or stoker voices 'coast' or 'butt break.'