This is a classic dilemma, which deserves a classic response. You state your age is 26 so as a young adult it may be time for you to grab the bull by the horns. This is not a teenage romance, but rather you and your girlfriend’s adult life. I think it would be important to talk with your girlfriend about how to approach this, but the bottom line is either you alone — or you and your girlfriend — need to have a meeting with her parents. Tell them how you feel. Explain that you’re caring for their daughter is genuine and that it is a joint decision. Explain that you would like to move forward with less friction but, whether or not they cooperate, your love for her isn’t going to change.
In other words put the ball in their court — yet make it clear that your love for each other is not going to depend on their blessing.