The in laws are a red herring, yes they may have caused the issues in the first place in regards to how they raised your DH, and probably compound that issue now with gift giving but ultimately your DH as an adult is now responsible for his own behaviour.
Many years ago I once worked 2 jobs, DH didn’t work at the time so I was the sole breadwinner, I also did all school runs and looking after our DC, I was stressed and exhausted. We started a business together, my working 2 jobs and doing DC care allowed us to fund the start up costs. DP’s parents gifted/invested some money to help during this time, and you know what I heard endlessly was how his parents helped us, but not how I had busted my ass working 2 jobs etc. This used to really piss me off, but then it dawned on me....my working 2 jobs was me just doing what I was supposed to do, it was expected, what his parents gave was not at all expected, it wasn’t their responsibility to help us, it was a gift and therefore was appreciated.
My point being is that his parents gift giving is their prerogative, and I don’t think it is necessarily wrong that they give their son more than they choose to give you. They are not responsible for the inequality in your relationship. It is not al all unusual for the balance and equality in a relationship to change once kids are born, especially if one partner places more value on the financial contribution over other inputs such as domestic chores or child rearing etc.
The crux of the matter here is that at the very root of things your priorities are different. You choose to put family first, you sacrifice yourself for your children/family and think of those needs before your own. Your DH on the other hand prioritises himself and his own well-being first, and from what I can see you are last on the list. 1) is himself 2) his children/parents 3) is you....your last. Very simply he places his value and his contribution above yours, and the reason why your frustration with his parents comes into play is because he counts their gifts to him as part of his worth/value/contribution to you/your family, yet you do not benefit from these gifts, because he reserves it all for himself because it’s what he thinks he deserves because he is entitled.
You are fighting a losing battle here OP, there is nothing and will be nothing you can do to make him view you as his equal. He will always believe he is worth more, it won’t matter whether you earn the same, or even if you were to earn more, (and I guarantee that if you did, he would only view this as you finally putting back in what you have taken out and so still not equal!!!) and even so why should you have to do that to be viewed as his equal? You don’t, you should be his equal regardless of your financial situation/contribution....you should be his equal purely because he respects you and loves you and as the mother of his children.
You didn’t win him, you weren’t lucky to bag him, he is not some prize catch!!! Just because a man may earn well and has generous wealthy parents does not make him a good man, good husband and good father. A good man, a good husband and father shares his wealth with his family, he treats his partner and the mother of his children as an equal, and he shows her love, care and respect!!! You don’t seem to get much if any of this at all, and THIS is your problem, not his parents because it is his choice to treat you as he does. It’s your choice as to whether you want to allow/put up with this, because you don’t have to, you do deserve more because being treated with respect and as an equal in the minimum bar, but also the most important bar to set in ANY relationship.