What multi-sig wallets are there for Android/Jolla?
If I go slightly of topic I will recomend you to incorporate a solution using a law of trusts if your law system has it incorporated. 

I am still about to recommend you Copay wallet as it is open-source. You can even rebrand it to your own company. 

You have to remember that you can use HD wallet with Copay. You can use Bitcoin Trezor with copay so you have strong security. And all of this could be saved to a secure place.