Jealousy is a normal, natural human emotion. Everyone experiences it from time to time, whether they admit to it or not. It doesn't make you a bad person and it doesn't mean you're not grateful for what you have the majority of the time. Beating yourself up for having a feeling doesn't get you anywhere, and it doesn't make the feeling go away. But if the feeling is uncomfortable or interfering with your day to day life you should probably try to address it.
Trains of thought around "how can they afford that and we can't?" are unlikely to be helpful. For one thing, you'll never really know. Even if you were rude enough to ask (not a good idea!) you might not get the truth. They could simply earn more than you, they could be buying everything on credit and have no savings, they could have accepted gifts from family. But what does it matter? Knowing wouldn't change your situation anyway. So dwelling on this is just feeding those uncomfortable feelings.
I think that you have two options. You can practice gratitude, focus on what you do have and remind yourself that there are good reasons for all the choices you've made, even if those choices haven't necessarily translated to an increase material wealth. Or you can actively try to change the situation, work more hours, go for promotions, relocate for better opportunities, sacrifice some time with family in the short term for hopefully for money in the long term. But none of those things are easy and you may not truly want that life, and just imagining it may help you to feel more contented with the balance you have now.
Have you seen the TV show Industry, OP? I found it really interesting in terms of it's examination of the psychology of people who are motivated by money and the pressure they put on themselves, the sacrifices they make and the impact on their personal lives and relationships. One of the characters talks about how life can become an endless cycle of "you covet something, get that thing, covet something else" and where does it end? Food for thought.