Andrew is correct you do have to be an actual car dealer/trader for this.
There are specialist Private Family Fleet or Multi Car policies out there for multi car households but they are not always the best way to insure your cars. If you insured them seperately you may find them cheaper dotted around individually.
We can arrange these types of policies, along with Traders Insurance and all Commercial Insurances, give me a call if you would like to discuss with me.
Thanks
Sarah
Neil Willies Insurance
Telephone 0800 542 0672