You are blaming a whole style of bike on your particular likes about fit on a bike. It's possible to change bars and stems to find a great fitting position on a drop bar bike, obvious as millions buy these and are happy. With a bike that currently has drop bars and wanting to convert to a flat bar you need to change a lot of stuff and it can be expensive. Better to have purchased a tandem that has flat bars from the outset. You need to change 2 stems, 2 h-bars, shifters and brake levers, likely the front derailer, rear derailer, hopefully not the brakes as well. You need to change essentially to a 2X mt. bike shifting system as the road shifters on the drop bar are unlikely to work with the derailers. Best bet is take it to a shop and have them advise. It can run a few hundred $$$.