For the examples given, I would argue that none of those are inflexion per se, except "from". As you note, English does have morphological inflection, but not all grammatical relationships are shown with inflexion.
I would say that "these" simply modifies "fish"; but also that I do not think "modify" is being set up as a "non-inflexional synonym". It modifies the totality of all individual fish by specifying a particular non-singular subset of fish that happen to be in close proximity to the speaker. We can contrast with "those fish" which specifies a particular non-singular subset of fish that happen to be somewhat distant from the speaker. Similarly, we can modify "fish" in other ways by size, by colour, by type, by sex, by gender, etc. So, inflexion is a kind of modification, but not all modifications are inflective.
I would also argue that English does have extramorphological inflexion. For example, we have a rich verbal system, that inflects (morphologically) for basically one person, sometimes for number and sometimes for mood. We also have a somewhat complex system of modal and auxiliary mediated inflexion.
- I mought could see to that.
- If she had only would've done this...
- She done gone spoilt the milk.
Your dialect may vary, but I would argue that these modals do in fact count as inflexion for English as much as any Latin synthetic inflexion. Long story short: English has (at least) two kinds of inflexion.