Not United Front With Husband Regarding Inlaws

Most of you all know that my husband is a shravan kumar..he tried to impress his parents and pamper them at every step no matter how they treat him, kids or me...nothing matters to him not even treatment to kids...my inlaws pretend to care for our kids in front of him but behind his back they are different personalities....
He realize that and stays quiet and tells me to be quiet as well ....It is killing me from inside as I see this everyday but somehow because they are parents its easier to digest and forget ...
But with SIL its the same thing and he fights with me for her too...So this shravan kumar mom has instilled this in his mind as to how he is supposed to do for his sister all the time...he finds reasons to give her...like he sees the sister for few hrs in an airport, gives her $500 , rakhi sends lavish gifts , etc etc...just reasons stupid reasons and give her so much money...I have had so many sleepless nights after fights with him...so I gave up on his gifting to sil as well ...now sil son...i cant take the fact that because he is sil son, he needs to be spoiled by us..we have 2 sons..my sil just send a gift on christmas for both of them together...no bday gift nothing...now sil sons bday, he has been forcing me to send gifts and last year i said that when she does not send it to us then why we need to...she just calls and talk to our kids and wish them, why cant you d o the same ? after all the fights, I had to send him a bday gift last year ...
this year too my kids bday went , nothing from her....now same fight happened regarding sending gift to her son...he was like its only 30-40 dollar thing.....its not money for me , its principles....i told him but we had a huge fight...I have started t give up just for the peace in my home but i'm so disturbed inside...it pinches me that our kids do not get any special treatment from his family - parents or sister as well....but I'm supposed to literally worship his parents , worship his sister too....and pamper her kid too....
I dnt know what to do , what to say and how to resolve this issue which I have been struggling for past 13 years..I'm so dne with this injustice.....all this would have been easy if my mil was nice to me, but she lies, manipulates and taunts me on my face ....