Re: B32 Yawl
I haven't come across much on yawls in my reading.
The 31.1 is an IOR rig, with a larger jib / smaller main, while the 32 has balanced jib / main, so my experience is not very applicable to your boat.
Generally speaking though, weather helm on my 31.1 sloop is mostly a product of heel and less of fore / aft sail balance, within reason (100% jib with double reefed main is tolerable) It is best tamed by keeping the sail area under control. Generally, reef earlier than you'd think. Don't overpower her with large jibs in strong winds. I find a 100% ideal up to 25 kts, and that with a reef or two in the main.
How old are your sails? Getting new sails made the greatest difference to my weather helm - better shape, less drag, less heel = less weather helm.
Bristol 31.1, San Francisco Bay