When you hover over हर दिन it gives "everyday" as a meaning. This is not correct.
"Everyday" is an adjective that means "normal", "mundane", "uninteresting", "not special", etc.
"Every day" is correct.
This is a very common error among both native and non-native English speakers but should not be in a language course like this.
Wiktionary mentions दादी means "paternal grandmother" while नानी refers to the maternal counterpart. There isn't any generic term for grandmas then?
We are talking about one grandmother or more than one? है and हैं change depending on the number of the subject. So why हैं? So the answer should be "Grandmothers eat every day" or what am I not seeing?
I try to imagine a context for these sentences. This sounds like a case of elder abuse: "Your grandmother appears undernourished." "But... grandmother eats every day... well...almost every day."