I would suggest, first speak to the old one and try to figure out why he/she does not want to go and then help him/her understand the important role he/she plays if he/she accompanies. Then speak to the middle one and maker him/her understand who's good for company or explain to him/her that this trip is more of a family bonding thing!...Finally, show the bright side of the trip to the youngest one!...Little ones only value the fun part, nothing more and they are easy to convince!...🙂
I am neither married not a parent!...That's the best I could do!...In case, it's not good enough then I am sorry!...🙂