Please do not get caught doing this, it is considered ILLEGAL if you're in Ontario. It doesn't matter if it is even the whole house just for children. The regulations are as you've mentioned are a maximum of five children per household or six if you're licensed through an agency. It doesn't matter how many adults are in the house taking care the children.

If you want to open a larger group between two teachers and more than five children then you must proceed to apply to open a child care centre. Also a Montessori diploma doesn't count to open a centre you'll need a Registered Early Childhood Educator.

The only way for you two and your groups to get together (playdates or teaching montessori lessons) would be renting a public area for few hours ex. Rent a room in a library, community centre, park etc. It has to be a public area not in your house.

Become familiar with the regulations of the province that you are, you will find it in the Web pages of the ministry of education the document is called Cceya (if you're in Ontario). There has been a lot programs closed like the one you've sujested, and another change also happening is that even big montessori schools need Ece's working in their classrooms.

I hope it helps.