VAT Registration

Hi can someone please help clarify something

My company is in the process of acquiring another company. We are VAT registered but the company we are acquiring aren’t as they fall below the VAT threshold.

Therefore my question is, if we acquire the shares of the new company do they have to join our VAT group or can they remain in their own VAT group therefore meaning we do not have to apply VAT to their trade until they exceed the threshold.