No you will not get in trouble.

Your visa is a “travel document” which lets you come to Canada. Your work permit is your status document. So as long as you stay in Canada during the validity of your work permit you do not need to renew your visa. You only need a new visa if you leave Canada and wish to return (by air/train/bus/ferry).

Yes you can.

He needs to write them an invitation letter and then their custodial parent has to apply for temporary resident visas (visitor visas) for them.

You should leave immediately. You can re-enter Canada legally later, when you qualify to come.

Yes, she should apply for a visitor visa. A letter would help the application.

1. She sends you an invitation letter inviting you to stay with her in Canada.
2. You book your trip.
3. You assemble the information necessary to show you will return to Nigeria at the end of your trip.
4. You submit your visitor visa application to the nearest visa office.
5. When you receive your temporary residence visa (visitor visa), you travel to Canada.

Yes, it’s a visitor visa.

No but your spouse won’t be able to apply for an accompanying work permit if they want to.

First he needs to apply and get accepted by a Designated Learning Institution. Once he has been accepted and paid tuition he can apply for a study permit and a visitor visa.

We wrote How to Get a Visa Invitation Letter in 4 Steps