I would have a good heart to heart/ blow out with her. Let her know that its just not that you don't want to let the kids have things, its against your relgion and explain why. Maybe she just doesn't completely understand it. I wouldn't leave it up to your BF. Alot of times guys don't like standing up thier mom's. Nothing is going to change if you don't stand your ground and express your feelings.
With my now ex husband's dad he would cut me down so bad! My ex was horrible with money so we decieded to have me run the check book. His dad would say what was right for "his" grandkids and didn't care what we did with my oldest. He would cut me down so much and tell me I was going to hell because I had my oldest when I was 18 and out of wed lock .. even though my ex adopted him.
It was not my place to have a say so in anything, run the money.. even know how much money we had at any given time. To put it simple my only jobs were to raise the children, cook the meals, clean the house and get a certian amount of money each week to go get groceries. Other than that it wasn't my place. He would treat my oldest horrible in front of him, say he wasn't part of "his" family. Would bring gifts for the other two boys, ask if he could take the other two boys etc.
After many times of talking to my husband about it I finally had enough when he was talking to us about something and I put in my oppinion about it and he told me to shut up I am a female and he will not listen to anything a woman says because I have no right to speak to any man directly. I looked at my husband and asked if he was going say anything or do I need to do it? He told me to let it go... well I didn't and there was a huge blow up.
A couple of months went by and after that he came by again and we actually have a good relationship now. Now that we are divorced and he is remarried his new wife wont let his father even around if she is there. His father and I have a friendship and he comes here to see the kids and will even bring things for my two littles with my husband now. He will take my oldest fishing just the two of them and do things special for him because he is older and able to do more things (even though he was doing the stuff at the age of the other two... its just his excuse to spend the one on one time with him).
I honestly believe that if I wouldn't have spoke up and put my foot down and showen him I hold atleast some of the power over the kids and his visiting and when I took them away he woke up. So sometime good things do come out of blow ups. Good luck and stay strong!!