Food for thought.. Money and sex are among the top reasons for divorce.

Suggest u have a heart to heart talk on life goals before tying the knot.

Marriage is also about the union of two families.. not only about you and gf.
Having the support of your in laws is always a positive.

As others have mentioned, try putting yourself in your gf's parents mind. It is natural for them to be concerned for their child's future well-being.

Communication is key.

Also i would advise you to consider carefully the habits and character of your future spouse. Is it in line with what you can accept for the rest of your life?
Don't go into a marriage expecting a partner will change for the better. If it does then thats a pleasant bonus.

One cannot change anothers character and behavior. That person must want to change it themselves.. then only will that change happen.