Is it normal to have regular sex with my mother-in-law?

For the past year I have been having sex regularly with my mother-in-law. I met my wife through an online dating app in the Bay Area 4 years ago. We have been married for 3 years. I am an average white male, 31 and my wife is Chinese, thin, short, and 28. We are into the swinging lifestyle and early into our relationship even before getting married we had sex with other girls and couples. Eventually my mother-in-law found out about our lifestyle when she moved in with us after we got married. She shocked both of us and said she didn't mind as long as we were commited to each other.
The first two years of marriage were great and my mother-in-law saw some of our adventures with other couples and girls which is probably why she and I eventually ended up having sex. A year ago my wife told me her mom was feeling really lonely and kept mentioning how lucky her daughter was to have a man like me to have sex with and share with other people. My wife asked if I found her mom attractive and of course I said yes. Her mom was 57 but looked like an older version of my wife. She then asked if I would have sex with her and after some hesitation I said yes. I had sex with her mom that night and it was some of the best sex I ever had. Most girls I wear a condom with except for my wife and my mother-in-law. My mother-in-law can't get pregnant anymore. The intimacy of skin on skin and cumming inside her is amazing!
I have been regularly having sex with my mother-in-law several times a week for the past year. My wife and I still occasionally swing. I have asked many times and my wife assures me that she is never jealous and is more than happy that I am with her and am with her mom.