Social Security is not considered a job, however, if you have other income it can be up to 85% taxable. So, his social security DOES count as income as does yours.
You can contact the Social Security Administration and have them withhold taxes from one or both of your Social Security benefits of you can choose to have an additional amount withheld from your job. When you select the step 2c indicator, don't forget to include your social security when determining how much you should have withheld.