As for who deputises for the PM - it's the current holders of the 'great offices of state' in order of precedence. That means first Foreign Sec. (Raab), then Chancellor of Exchequer (Sunak), then Home Sec. (Patel).
(I think this must be the first time in history that all three offices are held by the children of immigrants: respectively Czech, Punjabi Indian via Uganda, Gujerati Indian via Uganda. Odd to think that Idi Amin's expulsion of the 'Ugandan Asians' all those years ago would have such far-reaching influence on British life.)
And as for hierarchy I understand that in your system it means a lot...just as it does in ours (Vice President,Speaker of the House,Secretary of State,etc).
I'd would be interested to hear you explain how Jacob's intellect is lacking however.