Where the link is, is not an issue so much as where you want it to open. In any case, this (if I understand you correctly) cannot be done with HTML alone. If this other parent page is already open (in another window) and has a name, javascript can do it (however, being sure that the user hasn't closed this other window in the meantime is a major issue). If clicking the link is to open a page in a new window, the iframe on the page in the new window must have its src attribute set to the desired page, either via its HTML attribute or via a script on that page that activates onload of that page (or at least after parsing of the desired iframe). A parameter could be passed to a script on the page that is opening in a new window, to tell it what page to open in its iframe via said script.
Now, this type of scripting is complicated and will be useless to non-javascript enabled browsers. The same overall effect can be achieved using simple HTML though. Say you have a link on a page in an iframe. You want it to open a page (we will call this pageC.htm) in an iframe on new page (we will call this pageB.htm) in a new window, do this for the link:
<a href="pageB.htm" target="_blank">Link Text</a>
Then the iframe on pageB.htm can look like so:
<iframe src="pageC.htm"></iframe>