Dear Friend,
We also faced the same problem, when our company got split in to 3 different companies in 2008. Every company head had different thought of action for splitting employees, since many employees were common for the first company like Finance, HR, Accounts, Admin, Office peons, etc. Hence we discussed & deliberated with all new Heads to take it further. In 2 companies we have given appointment letter first to employees & immediately on next page taken their sign on resignation letter - just to assure that their services remain intact. In 3 company we have transferred their services new division with transfer letter. So, you just discuss this issue first with new Head of companies & decide best course of action without creating unrest in employees. Hope it is useful.
Shailendra Deshpande