Is the name Emilia (nn Emmy) too similar to my sister in laws name, Emma?

Not really. Emilia is pretty.

My partners son has a sister from his mum and stepdad called Mia and then about a year after she was born me and his dad had a daughter called Emilia 😅 if you like a name then go for it, I don't think it's too similar to Emma personally

No, I think it’s lovely!

If she has an issue she needs to talk to someone

Emilia & Emmy are lovely

Both names are extremely common so can't really expect nobody else to be called these names, I don't think she would be bothered.

Nah, they’re not too similar. Also bothered? If my sister in law called her child something similar to my name I’d be honoured!