When I ask how it's mounted, I mean is it directly bolted to the transom, or is it on a lift or other bracket? The tiller arm is the handle that comes off the kicker for steering and the throttle which I assume you have since you don't have a remote throttle and steering.
I've used this bar before in the past. It takes some tinkering to get everything bent up correctly. It's nice because you can pop the connecting arm off the ball joints easily when not in use. Downside is it tends to be a little noisy with rattles, and it also requires the two motors to be pretty much in the same tilt position when connected, but is very much cheaper than other options.
marinetech aux steering link
This is another option, looks quieter and is supposed to be more friendly to different tilts, but I'm not sure that's entirely fool proof. If it falls off where it's mounted, could easily damage a prop.
ez steer connector
Those two options will connect your steering.
Panther also makes some electric steer retrofits that steer the motor independently, you can also get a bracket for the kicker with tilt and steering built in.
panther stand alone option
panther kicker steer for their brackets
Panther makes many different setups, including brackets, tilt/trim brackets, with/without integrated steering.
For remote throttle control, you either need to run another control cable with another throttle handle, or use a servo controlled unit like a controllking
or a trollmaster
Controllking units are less expensive, and work well, but they are simpler. I used one (actually still have it in a box) and was very happy with it. Trollmaster has some more complex units that can also integrate with the panther steering kits, so you can have stand alone throttle and steering control in one unit. Very cool, but as you can guess, very costly.
If you want something that will work on the cheap, the first steering bar I listed, and a controllking servo throttle control will give you full remote through your steering wheel and a wired control box for throttle. That's the exact setup I used back when I had a kicker. Not as slick as some of the more expensive options, but it did work well.
I can tell you from experience, trolling with a boat (or just driving) without remote throttle control is very annoying. You can lock the throttle on your tiller arm, but if you're trying to hold speed constantly going back there to adjust the throttle gets old quickly.