Welcome Andy.

First off, nicely done for a hobby.

Secondly, there are others around here that are more experienced on this, but I will give it a go.

Yes the queen posts being directly over the ground posts would be stronger. Of course this would change your pitch since you obviously want 12' for stalls. (From what Ive read you want no less for the horses). Or you could change the height of the upper plate.

It also looks like (might be the perspective) that your loft is taller than your ground floor.

The connection at the queen posts (in my opinion) should be changed. That tie should probably drop so the queen posts join with the plate. It also looks that some larger bracing (more run) would be helpful.

I know you are wanting to build a scaled model (thus joinery is probably not an issue) but the connection between the lower pitch, plate, and upper rafter has always got me thinking. I think this might work. Extended tenon through queen to rafter.



Anyway, hopefully some others will chime in. This gambrel stuff has gotten a lot of discussion before.