What is the typical shelf life of grains and seeds?
Here is a site https://www.usaemergencysupply.com/information-center/self-reliance/storage-life-of-dry-foods#link7 which addresses many of the items listed, but unfortunately does not address the ones of most concern to you, the fattier items of sunflower and pumpkin seeds.

Flax they call a hard grain and put at 10-12 years with wheat and such.  Rye, oats, and barley they class as soft grains and 8-10 years in dry 70 degree temps.  Lower temps would extend.

I would think that pumpkin and sunflower would be considerably lower, possibly treated more like a nut.  For very long term storage, canning, or vacuum sealing may be an option for reaching the 4+ year stage.  I have had several year old nut meat which was canned then frozen with only minimum degrading beyond the initial softening caused by heating to can.  All long term storage will cause some degrading though.  To minimize, you would want cool, dry and no sunlight.