Did you manage to find a solution to this? The links provided don't apply to you because those pages only appear if you have an agency account.
I don't quite understand your problem with your target appearing on the wrong side, but I can help you with the other stuff you mentioned.
You can add more than one TM to your project, but you can only write in one of them. You have to choose which.
If you want to apply pre-translation, right after you upload your document, you'll go to a page that says "New Project Creation". At the bottom there's a switch looking button that says "Advanced Settings". Click the button to activate it and you'll see other options appear below.
One of the options is Translation Memory, so in here you will add your exiting TMs (but first you need to choose the source and target languages at the top of the page).
The last option is "Pre-translation". You need to do this after you have added your TMs, because you will need to click where it says "Translation Memory", select the first TM and choose what percentage of match you want to insert and if you want to confirm the segments.
Then click on the plus symbol below that says "Add Rule" and do the same again but with your second TM.
I hope this is clearer. Let me know if you run into any more issues.