Wayfinder builds the menus following the ressource tree. So if you want a portal page with option links to two alternative product pages, these should be child documents of the portal page in your tree. Example (with assumed document IDs 33, 34, 35):
__portal (33)
|__products1 (34)
|__products2 (35)
In the template of the portal you can use Wayfinder to create the option links:
[!Wayfinder? &startId=`33` &level=`1` !]
The parameter &level=`1` prevents the output of the children products1 and products2 in this list of options.
In the template for the product pages you need the following Waxfinder call:
[!Wayfinder? &startId=`[[UltimateParent? &topLevel=`2` ]]` !]
The UltimateParent snippet is looking up the tree to the upmost parent of the actual document. This would be "portal" here, so you need the parameter &topLevel=`2` to omit the "portal" in the Wayfinder output and let it start at the second level from the top, that is at products1 (or products2, respectively).
I hope that helps.
ottogal