For your Mum and Dad,
What are your Dads firstly for no reason have as his passion besides Mum. EG does he have a main interest or occupation a favourite something or longing, theme the pen to that if he is a car freak make him a pen looks like a Spark Plug top half etc etc. If Mum is a dandy sewer get some hand painted wood beads square face and drill them, glue them shape the top, bottom ones etc etc.
Need Ideas scan under your query having done your research under search. If you like talk to me by pm I have done so many themed pens.
Next thought get those pens of the shelf with family scriptures etc by taking them out of your top pocket as you give them and say more than once as you use these pens think of me and that you love them sometimes we wait and memorialise rather than realise.
Case in point I repaired a priceless Jade Frog Aens old he chipped a tiny piece of dropped on a hard tiled floor for a Chinese friend and later made a pen put it in a lovely box,bang straight into his lifetime Jade collection in the safe.
Have success,
Regards Peter.