Put the two images in one separate HTML file. Then there is page turn.
<newpage> doesn't exist. The 100% reliable way for a new page is a start of HTML file.
It's <br /> not <\br> and it simply does a newline (break) without invoking any <p> settings. Mostly should be avoided as CSS is used to change paragraph spacing, not inserting <br />
A <br /> might be handy to break a heading tag content on to two lines as you can't use a <p> and two separate <h2> tags or whatever can cause spurious spacing, extra TOC entry or even a page break on a conversion.
Never use <br /> to attempt a page break (a new file is more reliable than any "break" directive) or for paragraph or image spacing. Use css class with tag to set spacing.
Vertical spacing may not work well to centre. The margin-top may not work on first element of a file, but padding-top will. margin-top and margin-bottom work between elements, not at top and bottom of file in most cases.