Regarding page 5, it looks to me that is a rather formal, planned painting. So it could still very well be Ootori's idea to capture the more spontaneous moments on a canvas!
Edit: confirmed literally 5 pages later lmao
Also, what is this supposed to say? I can't figure out "This was the given with us".
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First, I would like to add that Ishikawa-papa having even the bad drawings of Ishikawa on his phone is a level of wholesomeness I wasn't expecting. Secondly, about the translations I have consulted the original Japanese and the original sentence is:
これが僕たちの当たり前だった Kore ga bokutachi no atarimae datta
Kore ga - This(the draw or in this context, this kind of style of drawing)
bokutachi no - ours
atarimae - usual; common; ordinary; commonplace; the norm
datta - informal past
i.e. Ishikawa-papa is saying that this style of painting was the norm, a given in terms of that you wouldn't even question it, that it was the natural way paintings were done. So there's no way to interpret it as the painting been given to them, what can also be understood by the context once he praises this new style of paintings he supposedly brought to the Ishikawa family or even vampirekind.
Hope it helps!