Hi Geeman, you need to speak to your broker about this right away before you do anything. Liability cannot be shared nor can any of us "sell" insurance coverage. If an insurer even finds out about someone offering to share their insurance they are at risk of having it cancelled outright. An insurance policy covers only the risks declared to the insurer when the policy is issued and adding any additional risk or exposure without clearing it with the insurer beforehand means that risk is not covered. If I have learned anything about insurance is that you have to be squeaky clean with your insurer. Insurance companies do not like to pay claims and before they pay out a claim they will do everything they can to make sure that they are actually liable under the terms of your contract with them, the policy. And even then sometimes it requires the policyholder to take further action such as hiring a lawyer to argue their case with the insurer. Tread very very carefully...
Listen to the advice above from Fireworks FX unless you are interested in losing your house and any other assets you have to a lawsuit.
Until 2 years ago it was possible for the larger companies to get a term on their insurance that would allow covering shooters using their product. After an exhaustive search, to the best of my knowledge insurance with the term allowing coverage to shooters from a company selling them product is no longer available.
In any case if this coverage was available your insurance broker would be able to tell you if you had it. Your best course of action is to talk to your broker and ask if what you want to do is covered under your policy.
Insurance through the The Institute of Professional Pyrotechnics of Canada (IPP) is about a thousand dollars for a year. So this is a much better option than risking losing all your assets.