Contract Condition dependant on another condition as mandatory at contract creation

Dear Experts,

I have a scenario based on conditions like below:

There are 2 conditions for contract type Residential like below:

1.Basic Rent

2. Service charge .

Here we need to make it as mandatory of these two conditions for contract :

and also If user added condition Basic Rent and for got to select the condition 2.Service charge ,then system has to throw the error message like Condition 2 is not added please add the condition along with the dependent calculation

Example :  1.Basic Rent:100

                   2.Service charge as 10% on Basic rent i.e. 10

I tried with default conditions for contract with Condition groups .

But still notable to achieve.

Could some can throw the light on this.

REgards,

Mohan