I cannot imagine the laws being that much different in Canada, regarding access and child support etc. Basic human rights are the same under the bill of human rights, yes?
I'd be telling her nothing! Work in the background as much as you can and find out what's legal and what's not. This woman will undo her own self but not quickly enough...right?
A few words of caution, though, kids can be tricky littls bu&&ers and they really might just think that the grass is greener on the other side? Just saying!
Does their dad have a custody agreement and is he paying child support?

After reading about what the Bm is like, I don't think that she would even accept that what she's doing is bad, another sad case of a person putting themselves before their children, I think that you are doing the right thing by documenting what happens Im sure that when the court hears how the skids feel about their mother it will be taken into consideration, your skids are lucky to have you, they need a positive female influence in their lives, the first time I was a Step Mum, to a boy and girl, their mother neglected them, the little girl then 5 fell over in the road, her leg was bleeding and she was soaked, her mother had chucked them out in the rain so she could screw her latest beau lol, her mother would'nt answer the door, so one of the neighbours took them in and phoned us, many other awful things happened as well, in the end their mother said she did'nt want them anymore, so we took care of them full time, it was like watching flowers open, all they had ever eaten was crap, they wanted, to eat fruit and veg, they craved it, I know it breaks your heart to see how Bm is effecting your skids, but I also know that they have 2 people who love them loads, so I wish you all the luck in gaining more access, hopefull full.

If she has email you should have BF write her an email about the problems he has with her parenting decisions. Be really fair about it (no cussing/anger) and make suggestions about what you want instead.

If she doesn't reply keep sending them. Refuse to talk on the phone or in person.

Her acting crazy doesn't mean much of anything if you don't have any proof that it happened. If she admits to it in writing it will be a problem down the road for her.

I have been through the Canadian courts and I can tell you this:

Topic A - The courts won't care - Her time is her time and Bio-dads time is bio-dads time. No court will force her to let the kids call whenever they want. Furthermore it is difficult to prove even with SS documentation.

Topic B - In Canada we have photo-health cards. Children are required to have their Health card with them when they are with either parent. She is not allowed to send you the children without their health-cards. Assuming you have split-custody, copies of birth certifs can be ordered online.

Topic C - Again, if it isn't during his court alloted time, the court will not change any standing arrangement to accomodate birthdays.

Topic D - Unless it specifically says in the custody agreement that she has to...

You can continue to document everything, but the family court system in Canada is different from what you see on TV or hear about in the states. It is kept very straightforward, and unless you can prove that there is abuse going on, it is difficult to change any exsisting agreement. Is their a custody contract in place atm?