Pycoin: How to send transaction?
Hard to say without looking at the code. Want to paste the relevant code?

When dealing with the GreenAddress api we generally sign using libsecp256k1 rather than pycoin (even when we use pycoin for other things)

For example see https://github.com/greenaddress/garecovery - it makes GA multisig transactions with pycoin and then signs them

Hope it helps!