My advice is to turn of RTE (Rich Text Editor), this can be done on your profile settings. Otherwise just put the picture in last, RTE tends to delete them if you open the page up for editing.
As for font size, if you turn of RTE (or use the source button [tho beware of potential consequences]), just use html tags. Generally you can google [how to do {thing} in html] to get answers, but for font just modify the attribute:
<font size="number">text.</font>
That aside, consider why you are using font changes + pictures, as while they can be used to enhance the reading experience, they can also kill immersion extremely quickly while also messing with readability. They don't necessarily have to do this, but most the time I've seen font style/size changes, I feel they were unnecessary. Just make sure it fits together properly and you aren't changing it just to 'be different'.
I'm not sure if RTE messes with font size tho, as I thought it could do that properly, but I wouldn't be shocked if it messes things up there as well.