Can a seller have the same house on 2 contracts?

[Jay Meola]

Hello all. I really need some immediate help.

Quick back story....

My mother in law has a house under contract which she will be paying cash. The HOA initially denied her. After contacting fair housing the reasons were deemed inappropriate and they immediately threw away the denial, (Within hours). The HOA contacted her and are having her resubmit all the forms, after apologizing to her for the "misunderstanding." They also contacted the sellers agent to notify them of the change. The closing date is set for the 15th of March. A few hours later the sellers agent calls her to notify her that the owner has had another couple sign a contract and set up an inspection for the following day!

I dont know much about this but this can't be legal can it? My mother in law is not working with an agent. Please help. Any and all 8nformation and advice is immensely appreciated.