Hi gevs,
just a few quick notes:
16: mandatory-script-verify-flag-failed (Script evaluated without error but finished with a false/empty top stack element)
IIRC this error pops up, if there are still signatures missing to satisfy the multisig script.
Missing inputs
Are all inputs still available or did you try to double spend one? Is your client completely synced, when you try to broadcast the transaction?
OP_RETURN 6f6d6e69000000000000001f000000002faf0800 OP_EQUAL
No need for the OP_EQUAL
Maybe I need a non-standard allowing node?
Omni transactions are standard. The only website still not considering OP_RETURN as standard script is blockchain.info. So be aware about this.
Here is a link to create simple send transactions with Omni Core:
https://github.com/OmniLayer/omnicore/wiki/Use-the-raw-transaction-API-to-create-a-Simple-Send-transactionIf you manage to follow these steps, you just have to figure out how to sign the transaction. To do so, you could probably import all keys into Omni/Bitcoin Core and then use `signrawtransaction`.