Moved abroad so travel has been much diminished this year and I am a bit out of the loop on what to expect now. Please reeducate me with the current rules on what to expect with lounge access, bags, seat selection, and SkyPriority?

4 pax total on KLM "light" fare: I'm Platinum Medallion (with no annual fee Delta Amex), adult no status, two year old, four year old
Outbound: MAD-AMS-BOS all KLM metal
Inbound: BOS-AMS Delta metal, AMS-MAD on KLM metal

I was able to add trip to my wallet in the DL app. Any other tips the community can offer?