We also faced the same problem when our company split into three different companies in 2008. Every company head had a different plan of action for splitting employees, as many employees were common for the first company, such as Finance, HR, Accounts, Admin, Office peons, etc. Therefore, we discussed and deliberated with all the new heads to take it further. In two companies, we first issued appointment letters to employees and immediately on the next page had them sign a resignation letter—just to ensure that their services remained intact. In the third company, we transferred their services to the new division with a transfer letter. So, you should discuss this issue first with the new heads of the companies and decide on the best course of action without creating unrest among the employees. Hope this is useful.
Regards,
Shailendra Deshpande