How to access ether.li multisig wallet, got private keys

So I tried to help someone get access to his funds. He gave me the required keys but all solutions I was able to find do not work or are offline (mist wallet, parity, gnosis doesn't work…)

Are these funds still accessible? And if they are, does someone know how? The owner promised a few bucks bounty if he can access his funds again (~2 Eth on the multi sig contract).

I am not dumb regarding crypto, yet never digged into Ethereum. So help would be appreciated here 🙂