I want to send assets from addressA to "addressB and addressC" in the same transaction.
We have a scenario such that,
A --> B ( 100 assets)
A --> C (100 assets)
if any one of the above fails, the other must also fail.
You can use raw transactions (createrawtransaction) to send assets to multiple receipients.Reference on how to build such requests: https://www.multichain.com/developers/raw-transactions/
The other answer is correct about raw transactions, but you'll find the createrawsendfrom API even easier and it will enable you to send sums to multiple users in a single call.