[Aga-chan]

HANABI

The "H" single was released in summer and refers to events that ayu connects with this season. (Except for "independent" which was recorded much before the other two songs.) "July 1st" refers to her day off (the birthday party, meeting friends) while "HANABI" refers to watching firework.
Firework in Japan, I think, symbolizes something beautiful, but short-lived - in this case it symbolizes love. Also firework looks like little stars on the sky...

Memorial address

I doubt that "Memorial address" is about her grandmother. It doesn't make sense. Because they had a good relation, ayu probably wouldn't have written about her:

I wish I could have heard from you
That I had certainly been loved by you
Only once, even if it had been a lie

You would only feel this way and say such things, when you have never known that you have been loved by a person. ayu's father left her at an very early age. She hardly remembers and knows her father, so she probably can't remember to have heard - or felt - to have been loved by him.
Maybe ayu longs to hear it from him - even if it had been a lie - because she wants to feel relief that he didn't left her, because he didn't loved her...