Seeking for advice.

Let’s answer each question separately.

1. Appeal can be withdrawn. Check with the employer A.
2. If pass gets approved and stick to company A then you need to exist then contract with B amicably. Tell the situation and circumstances during pandemic. They will understand.

But after your try if company B still insists to complain at MoM then they can do so. But in your defend you can show the email that you had tried your best to close the case with company B. Good luck

If you are very keen on doing this- Sign contract with Employer B with documented proof over an email, where you outline and explain that you have another offer for which the pass application is with MoM. State clearly that you would consider the job with B only if your pass through A is rejected, by MoM.

A contract, once signed, is legally binding and you have to fulfil it!
If you sign the contract that you will work for company B while while you still have a valid contract with company A, you are already in breach of contract the moment you sign. Do not do that - otherwise A or B are right to report you.
A must withdraw their work pass application (yes, it is possible!) right after you terminate their contract with them. So do that first (there might be notice periods or penalties involved - check your contract with A). Then sign with B and let them apply for your pass!