Hi Winifref2
If you have all the required documents and if your case if straight forward then you do not need a lawyer or law firm to file for your EE. All the details to fill and file your profile are available on the CIC website and on this forum.
If you have a complicated issue which cannot be resolved on this forum or CIC website then you should take the help of the law firm.
As for if the law firm is genuine or not that you will need to research online and check for yourself. You can always call and check the authenticity of the company by giving a call or checking reviews online.