My Wifes Idea

At the start of April my wifes mom Kim came to stay with us.
She'd not long lost her second husband in a car accident, so my wife invited her over.
After a few days I caught Kim masturbating on our couch. She immediately stopped and apologized, but I swear she made sure I saw her beautiful looking pussy first.
Telling her daughter later that night, my wife said this "She's probably lonely and has always been highly sexed".
My wife said it very matter of factly, almost as if she didn't mind me seeing her mom semi naked and playing with her pussy.
Kim went home the following day, but my wife had me drive her home.
This is where things got freaky. Just before we drove to my mother in laws, in front of her mom, my wife told me to make sure her mother was 'Satisfied' being home.
She stressed the 'Satisfied' and winked at her mom.
When we got to Kim's house, she invited me in, offered me a drink and returned from the kitchen naked holding a glass of beer.
Her comment was "The beer, or me".
A half hour later after some of the most amazing sex I'd ever had, I came inside my mother in laws asshole, after cumming in her mouth earlier.
We'd had oral sex, I'd tongued her pussy and ass. And we'd fucked both vaginally and anally in multiple positions.
Kim must have orgasmed over a dozen times, before we took a break.
She passed me the beer from earlier, and as I began drinking it, she slowly began sucking on my flaccid cock again.
We ended up in her shower, where she had me fuck her in the ass. I was absolutely shattered when we sat back downstairs. And only then did I see the messages from my wife.
They basically said I should make sure her I gave her mom 'Everything' she wanted.
When I got home, my wife asked me straight out if I'd fucked her mom. It was awkward at first, but eventually I told her what had happened.
I'd only seen my wife that ecstatically happy a few times before. And even though I'd drained myself, my wife and I had a wonderful long slow sex session on our lounge rug.
Since our first fuck, I've visited Kims House twice a week. Andc each time we've had sex.
It turns out they both wanted me to have sex with Kim, but when I didn't respond in our home, my wife insisted to her mom, she should seduce me in her house.
We've spoken about me having sex with her mom, and my wife has never been more at ease.
My worry, is it might one day cause jealousy between them. And I don't want to separate mom and daughter.
To that end I'm thinking of trying to involve both women together, but I'm not sure how to go about asking them.
I've tried to find out if they've ever been sexually intimate, but they're both coy about it.
They don't say they have, but they both don't deny they've had lesbian sex in the past.