Yes, you could capsize a F27 trimaran in 25 knots of wind with the unreefed main and
jib fully sheeted in. The most common cause of larger multihull capsizes is being over-canvassed and then making a mistake. Turning the boat quickly or steering into the waves the wrong way can both contribute to capsizing a multihull that is over-canvassed.
In a shallow river, if you have a situation where the wind is running against the current, you can get significantly higher waves than you would expect, and they can be very nasty to deal with and if the boat is being pushed hard, may be enough to get you past the point of no return.
When you're sailing a multihull in stronger winds and don't have her reefed for the conditions, the mainsheet should NEVER be cleated off.
You and your neighbor really need to learn to reef the boat properly for the given conditions, and sail her conservatively, at least until you have enough experience to understand the dangers and what is really going on. Years of monohull sailing don't really train you for sailing a multihull, since some of the reactions for certain situations are different for a monohull than what would be appropriate on a multihull.
BTW, you reef a multihull for the peak or gust wind speeds, where you reef a monohull for the average wind speeds. The reason for this is very simple—a monohull can usually bleed off the excess power of a gust by heeling the boat over.... a trimaran or catamaran can't do that. However, multihulls are generally lighter for the given sail area and will accelerate during a gust more than a monohull will, and need less sail in strong winds than a monohull does.
A beach cat, like your Hobie 16, isn't going to give you much real help in understanding how a larger multihull is going to react, since the beach cats are generally way over-canvassed, have a relatively narrow beam and relatively little floatation in their hulls. A trimaran, like the F27, will give you plenty of warning signs....but unless you know what to look for, you'll miss most of them and end up in trouble.
A couple of warning signs on a larger trimaran are:
1) If you start flying the main hull or the main hull starts to lift.
2) The leeward ama starting to submerge.
Also, while a multihull can go fast....sometimes it just makes sense not to go as fast as possible. I've been out in weather where we could have put up a bit more sail and gone 15-17 knots...but it is a lot more comfortable to reduce sail and cruise at 9-12 knots.
Finally, a common mistake and cause of capsize in multihulls often occurs when the boat goes from a downwind sail to an upwind one... The higher speed of a multihull often means that the change in apparent wind is far greater than it would be on a monohull in the same conditions. For example... lets say you're sailing on a dead downwind on a trimaran.
The wind is blowing 25 knots, but the boat is doing 17 knots, leaving the boat with an apparent wind of 8 knots. That same boat, turned upwind might be able to do 15 knots on a close reach, with an apparent wind of almost 38 knots—the apparent wind has over quadrupled due to the change in course. Now, unless the captain was paying attention, the boat is heavily overcanvassed and really on the borderline of capsizing.
A monohull in these same conditions, unless it is either a larger boat with a longer LOA or a planing design, would probably see 8 knots DDW with an apparent wind of 17 knots, and do 7 knots upwind, with an apparent wind of about 30 knots... or a bit less than double the previous apparent wind. Also, the monohull can heel to let the excess wind force blow off... the multihull can't.
A few good books for you to read:
Chris White's
The Cruising Multihull,
Michael McMullen's
Multihull Seamanship,
Thomas Firth Jones'
Multihull Voyaging,
In the video in the link, the conditions were 25-28 knots with gusts up past 35 knots... and 7-9' seas. 
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