Thanks for your advice, Jessica.Call (this isn’t something to rely on email for) firms B and C and see if they can offer a direct TC recruitment process or if they could whether they would still advise you to do the vacation scheme.
If they can’t offer one or advise to do the vac scheme instead to give you the best chance of securing a TC, the decision is made for you really.
You can accept firm A and then renege if needed.
I'm emailing now to set up a call with firms B and C this week. Do you think I should mention in my email that I received a TC offer from another firm?