I drove both and Model X. A good way to think about is if Model X has the space of a minivan, Model Y has the space of a mid-size SUV. Aside from space, Model X with the 6 seat configuration is probably the best car to transport multiple kids in car seats. The seat config of a Y will force you to place all 3 car seats in the back seat of a Y and because of less space, it's much more cramped if you need to get back in there to do anything Vs a 5 seat configured model X. The Falcon wing doors are easier for kids to get in and out which is a positive as well.
In terms of Cargo space for outings or short trips, I would say X has about 50% more room Vs a Y. For a family of 5, Y should provide enough room for everything.
There is no luxury in Y. It is as basic as it gets. X has a much more comfortable ride. It's more airy inside and kids will nap better during drives in the X.
Hope this helps.
Edit : If you are deciding between another Y or X, I would suggest to get the X. If you are replacing another large ICE vehicle and money is a factor, I would say, stick with ICE because Y is not a good experience WRT size for 3 car seats and 2 adults.