Finance and legal should be involved from the beginning of due diligence. That said, depending on the type of company being acquired, different key personnel should be involved. For example, years ago I was involved in the acquisition of an escrow office. Finance and legal where involved immediately but we also brought in key escrow officers to determine if processes were compatible and cultures were in alignment. The financials showed for a successful acquisition, but being that escrow is a very relationship based environment, it was key to determine if the staff was likable and skilled in their profession in order to continue success.