You have taken the good step of getting a lawyer, you should have the lawyer deal with all your concerns and work for your husband's benefit.
Yes your husband can be covered under the I-130 that was filed for his father and he can utilize the priority and adjust within the US.
The issue is that if his father didnt include him as his son on the I-130, you might have a difficult time convincing immigratiion to include him on there if you can prove indeed that its his father's son.
It is worth obtaining his father's file to have a copy of the I-130. When it comes before the immigration court, most judges will be sympathetic if the I-130 was approvable when filed, obviuosly it was. It is worht investing the time, effort and money to resolve this if you can get a favourable decision for your husband.