well considering the following:
- Recruiting said "brain power"
- Money required (now that can very wildly. which type of bomb, ways to deploy, how much testing, can know-how be "bought")
- Acquiring relevant material and infrastructure (both a nuclear power station and enough uranium, and then enriching it)
All of these, are difficult.
brain power - While Google probably has the best "brain power", non of these companies specialize in nuclear physics. could they recruit the necessary scientists for the right cost? probably.
money - now this is a difficult one. while apple has the most amount of cash lying around, is it enough? (they have roughly $90-$100 billion).
A nuclear power station can cost $15 billion. And that doesn't include the cost of uranium and waste disposal and so on. but we don't want to dispose of our waste, do we?
We also need to build a plant the can further enrich the uranium. After all, we do want weapon's grade (99% pure).
We're also going to need to manufacture the bomb casing (assuming the companies have the expertise or can't outsource it), buy the triggers (heavily regulated or developer it themselves which means testing out the bombs.
You're also going to need supercomputers.
What about delivery infrastructure? You could have a bomb, but how are you going to deliver it? A missile? A plane? Point is, all of this gets very very expensive very very fast.
Acquiring relevant material and infrastructure - And last but not least, all the relevant material necessary is highly regulated. From uranium, to plutonium, to the triggers used for nuclear bombs. It is ofcourse possible to get around everything, but it is difficult, and eventually the world will notice. I doubt it will be exactly easy for any of these companies to "legitimately" build a nuke".
So i don't think any of these companies can build a bomb. Only big government can "afford" it, get the brain power, and legitimize the fact that they need to "protect" themselves from other bad countries so they need WMD's.