Can a single step sequence instance map to two synths

Drum Maps might just be your answer to this.

There are several ways to do this.
One is in the step sequencer itself, the other by creating a drum map then loading that into the step sequencer.

Sending one MIDI track to two synths is no problem. Just select that track as the input to the various synth vsti/audio tracks.

If you set the synths to different MIDI channels you can then select which channel each step sequencer row outputs to. It is even possible go have several step sequencer tracks each playing the same note but outputting it on different MIDI channels if desired. The step sequencer help shows you how to set up the rows so that send the right note on the desired MIDI channel.

The drum map route has the disadvantage that you have to learn about creating drum maps and the learning curve can seem a bit intimidating at first. Once you get the hang of it though maps can be create very quickly and are permanently available to re-use as required. They can also be used in piano roll view if you find you need to do something more complex than the step sequencer allows. Again, they allow output to multiple MIDI channels.

My personal approach is to use drum maps where possible and once learned they offer a very powerful way to do all kinds of things with MIDI, going well beyond just putting drum names in slots rather than having to remember which note triggers which drum. On the other hand, if you've never made one and only need a quick answer for a single song then editing the step sequencer rows would be simpler.