having transited AMS 3x last summer (all KL online; Schengen to Schengen, Schengen to intl, and intl to Schengen), I'll offer that the 1-hour interline connection to the earlier DL AMS-SLC flight might well be a challenge for people who have unimpaired mobility if they're not particularly familiar with the airport
does DL still operate ATL-JAC on the day OP's parents are flying? if so, would the connecting time there be better? I tend to think an hour at SLC is doable, but my first choice in this situation would likely be to overnight at AMS