complaint about us discriminating based on familia

We received out of blue a letter from Michigan Department of Civil Rights,saying someone complaint that we discriminate based on familial status, asking for $10,000 settlement.

After much digging, it turns out the lady replied to a Trulia ad telling us that she has a fiancee with 4 children and looking to rent our bungalow. I replied her e-mail with a sentence: Maybe the house is too small for a family of 6. I didn’t receive any reply and assume she decided not to apply.

It turns out her daughter had made an appointment to see the house, but I didn’t know they are related at all. I went to the house but nobody showed up. So they interpreted my e-mail as a denial to show the house and filed a complaint with Dept. of Civil Rights.

Now the Dept. of Civil Rights is asking me to turn over the following:
1.) Names, addresses, and phone numbers of all of the applicants as well as copies of the applications

2.) Copy of all of the leases between you and your tenants

3.) List of all people you have rented to, along with their last known address, phone number, and number of individuals residing in the property

4.) When was the house built?

5.) When did you purchase the property?

6.) Copy of the purchase agreement, appraisal, and mortgage survey conducted at the time of purchase.

Should we hire a lawyer? Any recommendations? I appreciate all your suggestions.