He sure has

Over the coming months, Diah comes over regularly. Plenty are the times you use your mind trick to sneak up on them having sex. You no longer need to push them towards having sex. Once they’ve had their first time, they are much more open for more of that. While you do often pleasure yourself with Diah by feeling her boobs or fucking her mouth, you never stick your dick inside her vagina. That is reserved for Rowol. You regularly have to reapply the command to let Rowol fill Diah’s womb with his sperm. Or at least until one day Diah reveals she is pregnant with Rowol’s children.

Diah’s parents were first not happy with their child’s early pregnancy, but one visit with you and a few mind tricks and they no longer had any objections.
Since you were more financially stable than Diah’s parents, you allowed Diah to live in your house. That way Rowol could head off to college and get a degree while Diah stayed home while your grandchild grew in her belly. It is also around that time that you learn from your daughter in law that Chagrians are amphibians and stay underwater for several hours without having to come up for air. You also learn that Chagrians do not give birth to babies but tadpoles and require a tub of water to mature in.
Thus you started construction to increase the size of Rowol’s bedroom to add a large glass tub. Once ready you had it filled up with water and just in time, for Diah was about to give birth.

When the time came, it was a very private moment for Rowol and Diah (and you but you had mind controlled them into not acknowledging you). Diah took off all her clothes and with Rowol’s help got into the tub. There she swam. A naked chagrian female, only 19 years old, with a large pregnant belly ready to give birth. You and Rowol stood outside the tub, looking through the glass, seeing Diah in her full glory. Diah was on the other side, fully submerged and relaxed, like a fish in water. She opened her legs in full view of both her man and her father in law. Then she pushed and pushed until finally she pushed a tiny tadpole out of her vagina. You were surprised at how small it was. You had imagined for your grandchild to be at least as big as a human baby. But then Diah continued pushing and all of a sudden, a second tadpole plopped out of her pussy. The two little things immediately started swimming, almost as if they knew it instinctively. And just as you got over the surprise of having twin grandchildren, Diah popped another tadpole out of her pussy. She and Rowol have triplets now.
After giving birth, Diah swims up and hangs her head over the edge of the tub.
“So, what do you think?” She asks.
“Amazing.” Rowol answers. “I thought you’d be having one child but … triplets.”
“Didn’t you know?” Diah says with a smile. “Chagrians have triplets or quadruplets is just as normal as humans having one child. Having quintuplets however would be just as rare for chagrians as it is for humans to have twins.”
“Wow.” Rowol says. “So, how many sons and daughters do we have?”
“Can’t tell yet, my love.” Diah says. “We’ll have to wait until they are a bit more developed.”

Rowol and Diah continue talking for a while. Until their children start to get hungry. Then Diah dives back under water and gathers two of her children to come breastfeed from her. The two tadpoles wrap their mouths around her nipples and start sucking the milk out of her. After those are done, she gathers the third tadpole and lets it nurse from her nipples as well. You make a mental note that you should try out some of her milk yourself. To see if it is good enough for your grandchildren, of course. Though you do wonder which human traits these tadpoles inherited from your son. Oh well, time will tell.