Do not include in your return the full amount from your letter. If you are not claiming one of the individuals that you received the stimulus funds for, then do not report the stimulus amount for that person.
Your son should have indicated that he received the $1,400 on his return since you did receive the funds. However, the IRS has been matching social security numbers and he may have claimed that he did not get the $1,400, when the IRS checks his social security number against the database they will see that someone did receive the $1,400 and it will be deducted from his refund.
If you are filing MFJ with your husband then report that you received $1,400 and your husband received the $1,400 do not include the amount for your son.
