Hi Angela,
Not true with regard their tax, they simply ring up the tax office and ask to split their code. You will find some will transfer, some will try and dump you in it by saying they will transfer and then not turn up on the first night and some will want to stay with their current employer. It is a worrying time for cleaners when they hear that the company they work for has lost the contract so when you ask for the staff info from the incumbent supplier ask if they mind if you visit the cleaners to put their minds at rest. You also get a chance to see who you are getting!
Don't forget this is continuity of employment so if someone has worked there for 20 years previous, then this employment history continues with you. Also you will need to uphold all their existing pay and working conditions.
All the best
Tim