Is it Wrong to Keep Your Wedding a Secret From Family?

I apologize in advance for how long this is about to be.

So my fiancé and I have been engaged for a year and a half. We were planning on getting married at the courthouse on this Valentine’s Day and doing an actual wedding when we bought a house. He told his mom about this because we were gonna ask his parents and brother to be there at the courthouse with us, and she suggested doing a small wedding with his parents, his brother, my sisters, and a couple of friends in the place we got engaged. This was something we both decided we wanted, so we’ve pushed it back to July.

I have three sisters, and two of them are still underage. One of them is driving and will be getting her first car this month. They live with our grandmother about two hours away and we don’t want her at the wedding. She’s always been toxic in my life and we don’t want any negativity. We’re trying to see if we can have my sisters for a couple of weeks in July so they can be at our wedding, but we don’t want her knowing we’re getting married. Would it be wrong to not tell my grandmother about the wedding?