How can I fight for the sale of the property?

If your dad has died, you can file a petition in probate court to determine who is entitled to the property.

Inability to pay for your own costs is not a defense to the transfer of a home by will. Your only argument would be that either the will is invalid or that the will has been misinterpreted. You may need to take a copy of the will, if you can get one, to an attorney to verify that you are being fairly treated. Some attorneys will meet with you once for free to help you determine whether you have a case. If the home is a house trailer, it may be that the trailer is not in your Father's name, and needs to be distributed to someone else. If possible, talk to the last known owners to see if you can learn if they sold the house to your father.

On the very limited facts provided, you may not have any ability to force a sale. Is there a probate estate? If there is no estate, in Michigan, title to the vehicle would pass to the next of kin. In that case, you could go to the Secretary of State, sign the certificate saying there is no estate, and the title could be issued in your name (and your sister's). Your BIL would then need to open an estate in order to challenge this.

If he owns it, you can't fight it.