The tool can't be telling you that both Grandfather and you can claim Baby (or Mom) because only one can state they provided over 50% of support. There cannot be two people who can answer 'yes' to 'over 50%;'.
Also, Mom is not related to you by blood or marriage so unless you provide more than 50% of her support and she earns less than $4300, unlikely you can claim her.
go through the tool again.... be thoughtful how you are answering -
get beyond what you think your gut is telling you; go with the facts of the IRS tool.
