Help needed to understand direct hiring situation? Stressed

[NotAllThere]

Generally B2B contracts might have general handcuff clauses that applies to the employee working at the project/assignment which is my cause of concern at the moment.

Yes they might. But A, B and C are not going to reveal to you the details of their contracts with each other. Even if it potentially affects you.

Worst case, they terminate your employment, but you can't be sued, unless you are breaching a handcuff clause in your own contract of employment.