Possibly.
Your son-in-law can be your dependent if all the following are true:
1. No one else can claim him as a dependent.
2. He does not file a joint tax return with his spouse, or if they file a joint return, they owe no tax and they don't claim any deductions, dependents, or credits except for a refund of withholding. If his spouse (your daughter) has income and files a return, she has to file as married filing separately.
3. He lived in your home the entire 365 days of the year.
4. His taxable income is less than $4150.
5. You provided more than half his support.
You do not say where your daughter lived. If she also lived with you, you may have trouble with #2 and #5. It is almost always better for spouses to file a joint return, and that would override everything else.
For your grandchild, the following must be true:
1. He lived in your home more than half the year,
2. He did not provide more than half of his own support,
3. No other taxpayer can claim him, OR a parent could claim him but they agree to let you claim him instead and your income is higher than the parent.
Your son in law or daughter are taxpayers if they have less than $12,000 of income, and file no tax return or file a return only to claim a return of withholding and claim no other credits, deductions or dependents. If your daughter is a taxpayer and could claim her child, she gets first choice but can allow you to claim the child if your income is higher than hers.
