If you want to go electronic for some of the benefits of electronic, such as shift programming, crisper front downshifts, etc.,that’s great. However, something’s wrong with your current mechanical setup, it should work way better than that. Granted, my experience is mostly more-so with Ultegra / 105 / XT / XTR, and I think Tiagra is a notch lower grade, but still, it ought to shift better than that unless it’s completely worn out. How many miles on the Tiagra stuff? Shifters gummed up with old grease and not actually shifting when you move them? Lots of play in the derailleur pivots? Possibly cheap shift cable casing with a lot of compression flex in it? Something’s wrong. Others will no doubt be along soon with other ideas about things you could check. Again, if you just want to go electronic, that’s great, but don’t make that move because you don’t think mechanical can work properly. We have mechanical shifting on our quad which is twice the length of your tandem, and I never have to mess with it. My $0.02.