The best thing you can do is speak to a local estate attorney and ask the same question. However, just to give you an answer, yes, you can contest the Will, but its a long and difficult law suit if he was of sound mind when he made those bequests. That's the issue for Wills. Was he of sound mind when he made the bequest. The attorney who drafted the Will for him will more than likely testify in support of the Will since he/she prepared it and officiated over the Will signing and they have to uphold what they did.
In reality, there doesn't seem to be too much you can do to contest the Will since he mentioned you, however, your state's laws may be different than those in NY where I practice. That's why you should see a local attorney.
Unless you have some pretty convincing evidence that he was unduly influenced, or lacked capacity to know what he was doing when he signed the will, or that the will is otherwise invalid, a will contest would be a waste of your time and money. People disinherit their children more frequently than you might suppose; being disinherited is not grounds for a will contest. The "illegitimate" sister may have a claim as a pretermitted heir, depending on when she was born: she should talk to a local lawyer.
I agree with the above attorneys: a will contest can be a long, difficult and expensive process. I also agree with the point made that the "illegitimate" sister may have a claim as a pretermitted heir, depending on when she was born: she should talk to a local lawyer.
To comply with certain U.S. Treasury regulations, I inform you that, unless expressly stated otherwise, any U.S. Federal tax advice contained in this communication, including attachments, is not intended or written to be used, and cannot be used, by any person for the purpose of avoiding any penalties that may be imposed by the Internal Revenue Service. The information in this communication is not intended to constitute legal advice.
The information contained in this communication, including any attachments, is NOT privileged NOR is it confidential. It is NOT intended for any particular individual or entity, no attorney client relationship is intended or shall be inferred from this communication and that any reader is strongly encouraged to seek an attorney if legal advice is sought.