Qt LGPL Licensing – Qt, LGPL, Android, and Google Play Licensing

1. Signing the app I would generate a separate key for the company, and sign it yourself. The other company doesn't sound like it's at a technical level to appreciate the importance of a private. Also, I'm not sure what your agreement is, but they could at a later date ask for the keys used to sign the app they are selling. If you sign it with your own key, that means they could potentially sign other apps with your key and market them, something I'm not sure you want. If you're fine with sending the sources to the other company (with all the associated support costs of helping them set up a development system), it's a good option.

2. Licensing See above. If you have their key, you can sign apps as the other company, something they might not be ok with. Having each company handle their own keys presents the least potential for conflict.

3. Publishing This is the area where I'm least familiar with. I guess the answer would depend on your relationship - is this a one-off or the first of many? If it's a one-off, and you have a good relationship, you could ask for temporary access and do it yourselves; if you envision further work down the road, going through the pain of teaching them would make it much easier down the road.

Hope that helps!

Since you're using Maven, I recommend switching to the shade plugin to build your JAR. It can be configured to automatically handle multiple "standard" license files (see the section on resource transformers), and will warn you if your dependencies have overlapping classes.