I hope you are well today and thank you for your question.
Yes we can add it by developing custom code but you have to develop more code to display it somewhere so please advise whether you want to proceed just adding it.
To create such relations in portfolio you have to develop custom code.
Developing custom code for custom functionality is beyond the scope of support that we provide here. Please see https://themeforest.net/item/jevelin-multipurpose-premium-responsive-wordpress-theme/14728833/support
If you are not a developer then you can consider hiring a developer to develop it for you. You can hire a developer from any freelance site. Shufflehound recommends the developer https://www.upwork.com/freelancers/~011652ffec8865c6d5