BIP 44 master private key sign tx I have this Bip44 path implemented 

m / purpose' / coin_type' / account' / change / address_index 


Is it possible to use the Master private key to sign all the tx
ie. Bitcoin TX, Etherum TX

or do I have to get the asset based private keys for each asset and sign the tx's ?
or I have to get the asset based private keys for each asset and sign the tx's ?


Yes, you can't sign transactions using the master private key. Sign each transaction using the derived private keys.