Birthday Party Drama

I need some advice on how to tactfully address something without losing my cool. This might be a little long so I apologize. My husband and I are God parents to the soon to be one year old son of my husband's cousin. The father and his girlfriend are currently living with my husband's grandmother and are very young (early 20's.) There's many other issues going on there but way too much to go into here. So anyway, the baby is turning one in October. Yesterday I got a Facebook invite to his first birthday party for early October which would be held at my husband's grandmother's house. I responded I would attend and left it at that. Today, when I spoke to my MIL she informs me that the baby's mom (BM) told my MIL that BM's family is having the "big" birthday party and that we (my MIL & myself) should plan what we want to do for the smaller birthday party. So, I'm not invited to the bigger party (none of us are) and she somehow thinks it's my responsibility to plan AND pay for her kid's party!? This is not the role of godparents. Then, to top it all off the baby's father called my MIL today to tell her the theme they had chosen for the party and to remind her that they would need a smash cake. Apparently my MIL was so shocked that they ordered us to plan and pay for the party that she never flat out told them no. Now I'm stuck thinking of how I need to address this without being totally rude. Bottom line is, I have my own child who I plan and pay for parties for. I don't think it's appropriate for them to invite me to some party and then order me to plan and pay for it. I get the feeling that my MIL is going to give in an plan it anyway. Do I message the BM and address this or do I just ignore it since she never said anything to me directly and just show up at the "party"? How do I tactfully tell her I'm not paying for nor planning her kid's birthday party? Am I out of my mind here to think that this is incredibly rude? via /r/Parenting http://ift.tt/2vmLiMc