Hello my name is Jenny and I am happy to help you today. Is it your intention to reduce their hours?
Hi the difficulty that you have is that it is not possible to insist that a person signs a contract of employment. If they refuse to sign them then they may, depending on the circumstances, be deemed to accept the terms if they are working under them. Your position is further complicated given that these people have been taken over under what is likely to be a TUPE Transfer. Under TUPE you are not entitled to change terms 'in connection with a transfer' and a change in terms on that basis would be deemed to be unlawful by an employment triibunal. The only reason you would be entitled to change terms would be if you could identify an 'ETO' (Economical technical or organisational ) reason to do so, this would be something like a redundancy situation. I am not sure this applies here.
It seems to me that the best way of dealing with this may be performance management rather than giving out a new contract. Particularly if they are not up to the job.
If the people have been working for 20 hours from between 1 - 3 years it is likely that a tribunal would find that they are contractually entitled to those hours through custom and practice.
If you have any further questions please do ask.
No problem, all the best with it. Please do remember to rate my answer and do come back to me for further help in the future if you need to.