First of all just because few serial came to udaya doesn't mean it will turn as Sony . Sony and sun network had signed deal for sharing content. Already sun TV deal is over. Soon udaya will also be over.
And coming to company merge. There is no talks on Sony or sun combine. Sony had talks with zee for a potential merge. Which completely failed.
More recent is Sony eyeing on Reliance network18 's entertainment sector i.e viacom18 . And this deal is going in fast phase and finalize is also being done.
So in conclusion udaya or sun will not sell their asset to Sony.
There is no legal ban on dubbing. But the television association was forcing not to telecast dubbed contents. But due to lockdown situation all channels started telecasting dubbed contents.