Harley recomends you have your adjustable shocks on the highest setting (5) for that weight. You can buy a spanner wrench at harley for around 10-12 bucks.
The stock dyna suspension is decent and you shouldn't have any more issues riding 2 up. The only thing I miss on my sporty are the ease of the air shocks. I already put a scratch on my shock changing back and forth from 3 to 5, 5 to 3.

 

I'm 205 lbs, wife is 140 lbs, when riding 2 up on stock settings it would bottom out on the bumps. Cranked 1x notch away from max pre-load...no more bottoming out.

 

186 lbs, rode two up with a 100lb passenger and the shocks on highest setting, rode like a charm..crank the shocks up, thats why the springs are adjustable.

 

Thanks guys. Will adjust the stocks for now. I will start looking into the aftermarket shocks like progressive.

 

Works shocks. Perfection