I'm imagining how Randy told his mom about his new circumstances.
"Hey, mom. I died, but also kinda didn't. But I'm a magical kitty now! And also a father...?"
He was a wee bit more tactful than that. XD
For those wondering, the order of events from Viv's side is this;
She hears about a wildfire in Hoenn that, as she understands, is in the location where Randy worked for the lab. She tries to contact him with no luck. Naturally, she's heartbroken.
Suddenly, a short time after, she receives a call from him, explaining that he's somehow ended up in Sinnoh. He has no idea how, but that's where he is and he's... Well, he's alive. (He wasn't okay, as he was grieving for Akoya, in great pain, and still reeling from everything.)
As time goes on he contacts her once in a while, just to keep her in the know as he slowly improves. He lets her know that Lav sees him as her dad, and he doesn't have the heart to fully reject that. So they take her in as an honorary family member. He also tells her that Akoya is missing, and he suspects she might be dead. (He was too distraught to get that info to her in the first call.)
After four years have passed since the fire, Randy informs her that he's starting a League journey with Lav. This is the last she hears from him for a long while. (Also the last time he talks to her before learning what happened to him.)
Then, she gets a call from him saying they need to visit and talk in person.
And that visit is where he tells her what happened.
I haven't yet decided how long it took for Viv to accept him as Randy. But that happened before he and Akoya officially became mates and later got married, because Randy knew if his mom didn't accept him, he wouldn't be able to either. He was interested in taking Akoya as a partner before that acceptance happened, but he didn't want to string her along only to break her heart again.