I've been around Islanders a while and the brakes can be a real problem to bleed sometimes if the hydraulic lines have been drained.
If the 'O' rings have got to be replaced, the best way is to use a hose clamp as close to the union nut as possible and use a blanking plug once the line's disconnected. Take off the brake unit, replace the 'O' rings on the bench and fill it with an oil can. Then refit it and hopefully there's only five minutes of bleeding to eliminate the air. The biggest problem - BN having the bleed nipple at the bottom of the brake unit... no wonder air can't be purged easily.
The brake units have the option of interchanging the pressure and bleed ports so it's not Cleveland's fault.
To be honest, I think the Islander is pretty dismal in respect of some design and maintenance tasks as well as having inferior manuals, compared to American documentation. BN don't seem interested in improvements to anything.
Anyway, this thread is about the tragic incident, not engineering gripes.