Preserving ownership of authorship in the period after leaving a position and before journal submission
In the world of patent, researchers establish priority in the following way. They keep a bound notebook (no loose-leaf) so that pages can't be added between other pages. Whenever they have a good idea for which they want to establish priority they make a dated complete note of the idea. They then get a colleague to date and sign their note. At some companies most employees always have this patent book with them so they can record ideas as they occur. 

Then, if another person somewhere tries to patent the idea, they can present the patent book as evidence of prior art. The other person in this case may be completely unknown to you, but for patent, priority is pretty much the whole game. 

You can do something like this yourself, if you are unsure. It needn't be confrontational to your co workers. Make a signed and dated (paper) copy of each version of the paper that you work on and have a non-involved but trusted colleague sign and date it. You can even leave them with a signed and dated copy so that you each have one. 

The existence of these copies protects you a bit from being excluded. But in the absence of a problem, they are just private notes and so non-confrontational. 

For your future, you are likely better off with cordial relations with your co-authors. It may even turn out that they are proud of their association with you.