I dont know that part of the world but I think you should each carry 2 bottles of water each and refill along the way - no point in carrying more than you have to and you will also want to stop to view the scenery, take photos, talk to the natives etc. Your Mum & Dad should have racks on their bikes, with panniers or trunk bag - no back packs. Dont take any cotton T-shirts, only synthetic sports jerseys. Take several synthetic sport socks. If you dont wear cycling shoes, make sure the soles of the shoes are stiff and firm - thin soled sneakers = agony at end of a days riding.

All the load on the rack is taken through the bolts at the dropouts. The attachment at the top only provides a steadying effect, so P-clips around the seat tubes would be OK.

The 700c fork should be OK provided it didnt make a drastic change to the steering trail.