Ethics of/rules regarding submitting multiple presubmission inquiries
As an author I have done two presubmissions in the past. I do not know how they are handled by editors, but as an associate editor myself I gather they are informally skimmed by 1-2 editors within hours after submission. This means it is unlikely some "multiple presubmission" would be detected and I have never seen specific rules about priorities in presubmissions. 

Thus I think one is safe from editorial action if "caught" in multiple presubmission enquiries. However I believe it will not be seen with good eyes by a handling editor, and might leave a bad impression. 

Thus I would not recommend doing it. Particularly as an editorial answer usually comes in less than 48h.