1. I think they might say that you could also send your mother money if you were working in Canada. However, I can not say for sure what they will tell you or what will be accepted. Maybe they would accept your reasons.
2.-3. I have heard of PR cards being confiscated but as far as I know, there is actually nothing in the rules that allows them to do that. If somebody accuses you of not meeting the residency requirements, you tell them that you are forced to stay outside Canada because of your sick mother and you will give evidence of that when the time comes to renew your PR card. If they want to confiscate your card, ask them to show you what section of the IRPA allows them to do that. I know a woman who was a Canadian PR but moved to the US. As she went back to visit, an IO wanted to confiscate her PR card but she protested and was allowed to keep it.
4. If you enter Canada while your PR card is still valid, they will in most cases let you in and tell you to clear up your issues as you apply to renew your PR card. If they decide to report you for not meeting the residency requirements, they could do that in which case they will still let you enter Canada and give you some time to put your appeal together.
5. If they ask for your passport, you would have to show it but if you already admit that you didn't meet the residency requirements, it might not matter. If you do not have your passport any more and they want to know your travel dates, you should try to use whatever you have to support your claims. If you still have your passport but know you have to give it up, for example for renewal and that you will not get the old one back, you should have certified copies made before you give it up.
6. They have recently talked about taking up exit controls to catch PR's who make claims of having lived in Canada when they didn't in order to keep their PR or apply for citizenship. I guess they must have started that now.
You should read the manual on permanent residency status determination. You can find it here:
http://www.cic.gc.ca/english/resources/manuals/op/op10-eng.pdf