A trust is a document that holds assets of the trustor (grantor/settlor), in trust for the beneficiaries named, all to be managed by the named trustees. If you list your dad as a beneficiary, he is exactly that. The beneficiary of the assets listed (usually spelled out how it will be managed or divided up.) Usually one has named a successor trustee to manage the accounts and assets and then administer to the beneficiary before the trust is dissolved. If you don't have any living co-trustees with yourself or any successor trustees then the trust will usually be handled by the executor of the estate, which could mean probate. Any way you put it, the trust eventually dissolves and that means the assets, such as NFA items, will need to be transferred to your father's name, else it would be illegal possession as the trust is no more. That being said, I would think you'd have plenty of time to transfer it to a new trust. The only issue is the beneficiary cannot manage the assets and therefore cannot fill out the Form 4 in order to transfer it to his own trust. Which is why a successor trustee is vitally important as they have the legal signature to sign the Form 4, naming your father's trust or just his individual self as the new owner. Pay tax and wait 12+ months later and he can take legal possession of it.
Or you could simply amend your trust and make him a trustee. A revocable trust is supposed to become irrevocable upon death of all original trustees. I'm not sure perpetuities are allowed but I wrote mine in such a way that it is supposed to. Probably wouldn't hold up under legal standing but I'm more concerned what the NFA desk jockey thinks (and doesn't know,) not a fight over the few assets within in probate court.
Sole beneficiary simply means one or only. You can have as many as you want.
You are the grantor of the trust, only your signature is needed. Beneficiaries typically are unawares of trusts so, no, he doesn't need to be present.
Don't know how to answer that question. There are many parts of a trust needed to be valid.
Sure, anyone can use them. Possession means ownership. Doesn't mean physical, momentary possession. However, for storage and ownership, only the trustees can as each one of them can manage the assets of the trust.
i am not a lawyer in any shape, way ,or form.