Which immigration office? I have never needed to do this for the income affidavit. Due to Thailand (as well as China) not being a signature to the Hague convention legalisation of documents is a pain.
Mistake 1 you did not call your insurance, mistake 2 you don't have a police report and mistake 3 you asking advice on FB. Phone your insurance and talk to them. You could face paying the womens medical bills because you didn't follow the rules for handling accidents in Thailand.
BDB can confirm the shareholding of companies and who has the authority to sign on behalf of the company. The Chanote shows the owner of the property and that must correspond with the company details if the house is owned by an individual confirmation of ownership is even easier. Just be aware that liens against a property are also noted on the Chanote. The best is to employ a lawyer if you can't read Thai.
If you meet all the requirements and you have a few hours available each year do it yourself. If you use an agent you will save time at a hefty price and could be scammed in the process.