Why do you think the royal family was executed?

officially, According to the official state version of the USSR, former Tsar Nicholas Romanov, along with members of his family and retinue, was executed by firing squad, by order of the Ural Regional Soviet, due to the threat of the city being occupied by Whites (Czechoslovak Legion).

But for me its the mostly the same, they were a threat and well.. "needed to be taken care of". If you recall the guards watching over them were drunk and apparently took them into the basement for the execution.. but yea.. they were a threat to the current ruling power..

punish germany and keep it weak,

to extend a country’s power and influence