I disagree with your husband and agree with you. Each child should be parented in such a way that they are successful for his/her abilities and ambition. That is definitely not the same for each child. My in-laws were experts at this, raising five children (4 adopted, 2 special needs). Let me illustrate...
My husband, by the time he was 17, showed my IL's that he could take the car out, not wreck it and be home by curfew. His curfew was lifted because he had shown responsibility and he continued to make good choices even with no curfew. My eldest SIL, by contrast, lived at home until she was 20, and NEVER had curfew lifted because she could never get home on time (plus she had a habit of wrecking the car). She never showed the responsibility and even now, nearing 50, she STILL can't show up to anything on time. We all give her a start time of 30-60 minutes earlier than required so she'll actually be on time!
My sons are like your children. My eldest, starting his senior year, is a scholar. He's currently 2nd in his class and is looking to attend university to be a vet. Obviously, we're hoping for lots of scholarships but we're preparing to pay what we can. My youngest, by contrast, has wanted to be a Marine since he was 7 years old. Then, he wants to be an engineer. As he once told me, "Mom, I want to learn to blow things up, then learn how to build things better AND then be an architect to make them look good." Not sure I like the "blowing up part," but it's clear he may be better off enlisting straight out of high school and pursuing college when he gets his adventurous wanderlust out of his system. While I'm WILLING to help him pay for his college education, HE may not need that from me. What he may need is for me to support his choice to be a soldier.
As for gifts, my husband and I try to keep things balanced, although some years there is disparity between what the boys want. In our family, each boy got to choose a huge family vacation as their present for their 13th birthdays. My eldest chose Disneyland (over $3000). My youngest choose a couple of days of whitewater rafting (about $1500). Both boys swear THEIR 13th birthday was the best family trip ever. By your husband's standards, one got ripped off because his vacation was half the cost. But, according to my boys, both presents were perfect...for them. Put another way, if one kid gets a $200 piece of electronics, they other kid might get roughly $200 worth of other gifts. I'm ok with that. But, if one kid *really* wants an expensive gift and one kid *really* wants a less expensive one and they both get what they want, well, both are happy and that makes me happy.
Sounds like your husband's parents forgot that each twin was truly their own person with individual needs. I hope you can help him out of that outlook.
Good luck, dear mama. It's hard to unlearn things we grew up with from childhood.