Combining the Tyros and the BK would be difficult by themselves. Simply put, the Yamaha's simply aren't designed as flexible MIDI controllers.
Your better bet is a two keyboard system, with a controller keyboard on the bottom, for Roland arranger section and both Roland and Yamaha lead voices (get a controller with two independent MIDI outs), and the Tyros for control of its own arranger section and just Yamaha lead voices. Yes, you CAN get the Yamaha to control lead voices in the BK, but it's a PITA and convoluted.
Ideally, a 76 bottom keyboard and the T2 as top, you've got a pretty good system there. But having the Yamaha play some Internal voices for a style and some external on the BK would be tricky. And vice versa, TBH. Plan on doing a LOT of detail style editing if you want to achieve this.
It might be interesting to clock the Yamaha from the BK (or vice versa) and have TWO styles going on at the same time, and just use Part mutes to select which one plays which Part... But getting them both to change Var's and fills is going to be tricky. If you can find a master controller that will allow ONE button to send two DIFFERENT MIDI commands on different outputs and MIDI channels, you might be able to pull this off. Sadly, no two manufacturers use the same MIDI codes for the exact same function
But a BK from a T2? I doubt that that can be done satisfactorily unless you want only the very minimum communication between the two.