Stepdad changed their will same day my Mom buried

My Mom married to stepdad over 31 years, called himself my Dad for 37 years. Rewrote a new will 5 and 1/2 years ago the day my Mom was buried to leave everything to his 2 children from previous marriage. Do we have any rights to contest as she told us everything had been written to equally distribute to his and her kids upon both of their deaths.
His kids rarely kept in contact over the 37 years we knew him and insisted on his will being read the morning of his funeral.
In the will he stated he had 2 children and 2 children only and was leaving all to them. He never took my Moms name off the house and land but did file her death certificate and did change all her savings and checking accounts the week she was buried also.

You will have to have some good reason--he is free to change his will and exclude you unfortunately.

...seems a bit odd however...why would he have done that?