Serious question here.

I need some advice and answers in some way possible. So we all know it’s tax season. Okay so I’ve been with my fiancé for almost 5 years now he is 32 and I am 25 I will be 26 this may. We have three children together and one on the way ❤️ when it comes to money or paying bills or putting food on our table we both do what we can to get by. I am a stay at home mom only income I do get is child support for my eldest and my fiancé works full time 18 dollars an hour job. When it comes to money I don’t ever ask him for a cent or even touch his wallet or anything ever I have no access to his bank accounts. I am the type that I don’t like depending on others I’ve never been the one to get things handed to me on silver platter. So back to the taxes so my fiancé does his taxes with his mother and “step father” he’s been doing this for idk how long but to me it’s just weird because he is a grown man but he lets walk all over him from what I’ve seen. Now every year his mother always has to include some Primerica thing which he has no idea what it is and his mother won’t even give him any kind of info on it whatsoever so every years she waits for some sort of letter to give to their tax lady and then he’ll be able to get his taxes in the next few weeks or so he claims all of our children he probably only 6900 for taxes now to me and my mother we think he should be getting more and I feel someone is taking money from him. Now I love his mother and family very much. But I feel like he being lied to about something and if they are taking money that is not right without his say every year it’s an argument because by now we should’ve bought our own house already and not struggling financially just to get by. Now am I being crazy or is his mother taking money from him in some way I mean he’s 32 years old he’s not young and we live in a 3 bedroom apartment and have one vehicle.