S&S is the first that came to mind. I have some great stories there. Right now he's stuck on the Columbia models. He's also thinking ketch or yawl rig. He'll have a learning curve with either rig.
For the Transpac it would be he and I. I've done two passages (NOT Transpacs) with a two man crew so I know it aint a reach (pun) to be 'short handed'. The 'round the world would be us two as well.
I'm fairly against multihulls for long legs. Plus they don't beat as well. But my experiences there are +20 years old...maybe something newer is out there.
To bring us both up to speed I would suggest a couple Baja HaHa and a Newport to Ensenada in full race mode.
The Bill Tripp Columbia 50 isn't bad, and one of the originals of the design built IIRC as the Oceana 49 was a yawl. Here's the deal though, you'd really, really really like a wheel house, pretty easy to do with a Columbia 50. Thing about those boats though, they're slow, brutally slow. I used to beat them in races with my Catalina 27.
I've done a few multi hulls. In the very begins of my career at sea back in San Diego there was this big circus came to town looking 75' catamaran, Fairweather One, that was built in the early 70s out of what looked like construction site scraps in AZ and was built by a bunch of hippies using a National Geographic article for the plans, s--t you not. That was my first delivery job from SD to PV, and I had been sailing about a month at this point. Boat was complete POS we got into weather, I had to go up the mast in weather, we had no winches (I did have Chuey though, and Chuey was better than any damn winch), one engine blew up(port), the opposite rudder broke, ughhh, just ugggg. I slept in my wetsuit several nights. We got there just fine, and even though we had a filthy bottom (didn't want to risk peeling the plywood) we maintained 12 kts the whole way.
When I was in Aus, I delivered a high performance 12 meter cruising cat from the Perth area around Cape Leewen and over to Adelaide, and we were surfing nicely in 20-30' following sea. It would start getting noisy at 14 kts and be deafening at 18kts as the bow wave starts beating into the cross deck, but dude, we rocked and were perfectly stable in 50kt winds in the Southern Ocean. (I have done the S.O. in mono and multi hulls, and if I'm going back under sail, it will be multi and big)
We did have an issue with the anchor point for the headstay was poorly designed and executed, and nearly broke and did so only after sitting secured to a dock.
As we pulled in:
Notice the entire side is cracked loose, and it's a tab that is only surface welded, and this was a fresh repair and new headstay.
A few minutes after I took that picture which was about 15 minutes after we tied up, this happenned:
Notice the press swage, I objected to that when I arrived at the boat in Perth. Also, all but about 5 strands show prior damage and fracture. Those five strands held a hell of a lot, and they held till we were tied up.
This is the bow fitting I built for the boat:
That's what things need to look like for the Southern Ocean.
Double handing around the world? I'd be all about an 80' wave piercing tri. Here's the thing, speed is your friend, especially in the quest to chase the beam reach winds around the world. You need to be able to do sustained runs at 15kts to keep yourself where you want to be in regards to weather. If not, you've got to be ready to button up tight. That, and 18kts gets you around the world and across oceans quickly. I'd rather be on an ocean racing style multi for 7 days than a 70' mono for 30. Lot less supplies required. Big spaces at sea are wasted and hazardous, and slow you down. Small spaces are more sea friendly as you don't get thrown, at least not too far.
Just remember, if you're double handing, and you get caught in heavy weather, the odds say you or your brother or both will sustain serious injury or death. Thing is, in heavy weather you have to drive to the wave coming, and the autopilot can only drive to the one it's on, so you have to hand steer the boat. In heavy weather you can only steer for an hour at a time, it's physically demanding, and after about 12 hrs as you're in the heart of the storm, neither of you will be able to drive anymore and that's when the trouble is going to hit. So for you guys, I say get the fastest freakin boat you can so you can keep the weather where you want it, and that means multi. Y'all can build one. An 80' ocean racing tri is a remarkably small and simple to build boat, and there's probably a few out there for sale pretty cheap. Build out as much interior as you need and no more. Remember, you're gonna sleep, eat, read and stand watch mostly, do the crossings fast and use the money you save for rooms at resorts. There was a Sydney Hobart race around a decade or so ago where heavy weather hit. It shows quite succinctly what happens to shorthanded boats in heavy weather.
Oh yeah: