Not Mentioned in Will

My father wants my 3 siblings and myself to give his current wife a large sum of money from the sale of the house after his death. The house is our part of the inheritance. My father is not putting this in the will as he is an invalid and doesn't want to go through the process, but wants us to "promise" to give her the money. My 2 brothers agree, my sister thinks she should only get a small portion, and I disagree with giving her anything. She will already be getting his pension (currently worth over $2,000), his social security check, all the house furniture, a new car, and a bank account in her name, currently worth @ $7,000. I think this is more than enough, especially since she comes from a very wealthy family and stands to inherit a very large sum of money upon her mothers death, which could happen at any time, since she is very old and sickly.

My question is: if it is not in the will, am I legally bound to hand over my share of the amount from the sale of the house, or can I contest this?

She may have some rights by law to a partial interest anyway. You really should have counsel draft this up for you. A local wills lawyer will charge about 200 dollars and save you all a great deal of frustration.