Dear Rahul, please note the following:
a) If the rules of your organization permit, then there is nothing wrong with moonlighting per se. Therefore, please check the provisions of the appointment letter first. However, most companies do not allow their employees to take on a second job.
b) The additional factor to consider is your health. You are already working at night, and night duties are more strenuous than day duties. If you are spending 9-10 hours in your regular employment, including time spent commuting, when will you rest and do household chores? Your second earning should not come at the expense of your health.
c) Even if you take on a second job surreptitiously, inform your employer to categorize you as a consultant. When invoicing, you may use the name of a non-earning family member like your mother, brother, or sister. However, it remains to be seen how branded or organized companies will allow this type of arrangement. With GST in place, the company will have to treat you as an Unregistered Dealer (URD). Nonetheless, the company will not incur financial loss due to URD as they can claim input credit.
d) If the company designates you as a casual employee, the post-GST rules are unknown to me. However, the company will have to pay 4.5% ESI on the remuneration they pay you. This will be an additional burden, and they may seek to recover this amount from you.
Lastly, let me comment on your post. Besides your regular employment, you wish to take on extra work to fulfill family obligations. Your commitment to your family is commendable. Your post reflects the strength and integrity of your character. Keep it up!
All the best!
Dinesh Divekar