Though they are only 7 and 11 I would talk to them.
I would highlight they are loved, they are brave. I would then ask them what would be best way to reward them for good behaviour and recognising bad behaviour.
With the loss of their Dad they hav experienced loss of control. Maybe mention whether they like schools system my daughters primary school has dojo system. Also include family rewards. No conditional. I would also look at opportunities for emotional release. The three of u are possibly trying to be brave not releasing sadness, anger, frustration a safe form of release is key.