According to the information you provided, I think:

First of all, there is no doubt that the gas company has a gas supply contract with A (otherwise, the gas company will not take the initiative to help a non-contractual party spend manpower and time checking the safety situation). In this contract, it is the obligation of the gas company to check the gas safety, and the gas company's inspection at A's house is the act of fulfilling its obligations; On the other hand, the gas company carries out inspections for the safety of the parties, and Party A has the right and obligation to provide convenience for the staff of the gas company to check the safety situation. Therefore, it is also a breach of contract obligation for Party A to refuse the staff of the gas company to carry out safety inspection on the grounds of "inconvenience".

Secondly, it is also a violation of contractual obligations to let the staff of the gas company sign on their behalf. The inspection of the residence by the gas company is a contractual agreement between the gas company and the residence. According to the relativity of the contract, Party A can only confirm and sign the inspection of Party A by the gas company, or Party A can entrust others to sign it in writing. In this case, the staff entrusted others to sign on their behalf, which is similar to the above-mentioned "A entrusts others to sign in writing".

To sum up, I think that it is a breach of contract for a company not to provide convenience for the staff of the gas company to check the gas safety situation and to ask the staff to sign it on their behalf; Secondly, it is also a breach of contract for the staff to persuade neighbor B to sign a contract, because B is not a party in the gas supply contract between the gas company and A, and can be considered as an unauthorized agent, which has no influence on this inspection certificate; At the same time, this kind of behavior of the staff should also be in violation of their duties, and should also be punished within the company (I don't know how many punishments). In this case, if there is a safety accident, both A and the staff are responsible. In principle, they should bear half the responsibility, but in practice, the court may handle it differently according to different legal facts.

In fact, in this case, the staff should refuse to sign on behalf of them, announce A's refusal to check, and ask neighbor B to testify, or record A's refusal to accept the security check in writing. In this way, even if A doesn't sign, it's also A's own responsibility. The gas company has done its duty as a reasonable obligor, but A's lack of cooperation makes it unable to fulfill its obligations, so it should be A's responsibility to have a safety accident (unless the gas company has a problem with its own gas supply).

I hope my answer will satisfy you!