**Adding this:
A baby/child, also can get over-stimulated and overly bothered.
Then they will pull away. Or get fussy (because they don't talk succinctly like an adult nor have the vocabulary yet).
So, I would tell Grandma, not to get so hovering. Again- a child this age and even until 3 years old, they do what is called Parallel-Play.
And if your child needs space, then Grandma needs to do that.
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I would not, "expect" a child this age to greet other people with hugs and kisses. Nor make him do that.
Kids this age don't even know social rules and they don't even have social skills yet.
Kids this age do what is called "Parallel Play." They do not interact nor play, like older children. Children parallel-play... even up to 3 years old And this is normal.
At this age, personally, I would not make a child have to... give hugs and kisses to someone, if they don't want to. Your Mom should not get offended. This is about child development. Your child is only 1 year old.
For me, I went by my child's cues.... and did not want them to feel they HAD TO kiss/hug someone if they were uncomfortable or did not want to. Why? Because I wanted them to know themselves, and about how to follow their instincts.
Now, at this age, there is also separation-anxiety and stranger-anxiety, and so MANY phases.
So many phases.
For example: my son when about your child's age, he was SO afraid of an Uncle. Even if he knew him. Why? Well, because this Uncle has really unruly crazy bushy hair. And he looks like a caveman.
Oh well.
And separation-anxiety, is something that occurs at MANY ages... and it is manifested differently, per age. It is not just in babies.
Then well, I assume your parents are kid friendly, and good about child care and safe and caring.