Kids move at a much slower pace and need regular breaks/naps. Don't forget to plan for this when you travel. Try to do most of your activities in the morning and have the afternoon to relax. Thinking that you can relax on the beach for the whole day is simply not going to happen. Although, I guess that is why Kids Clubs exist ;)
Pay the extra money and book separate rooms. You will all need your own space. You probably don't want to go to bed when your kids do either. After a long day of travelling you need to unwind and relax with out being interrupted for 5 minutes. Your kids are the same, unless you want to watch repeats of Paw Patrol or fall asleep with the theme song in your head. Book a separate room. After all your on holidays.
Cheap flights are often at random times of the day that might interfere with your kids naps or moods. They often don't include checked baggage or seat selection. And can sometimes leave from a smaller airport that may be located outside of town. So consider the extra travel time and costs here. Are you really saving that much?
Ensure that you do not have any major activities planned for the first 24 hours after you land. Especially if the flight more than 8 hours. This will hopefully allow your kids to adjust to their new time zone and be ready for the adventure.
Take time with your packing. Think it out, often when you are rushed that is when you over pack. Think about Want Vs Need. Try to book accommodation that has laundry services. This will save you on lots of packing space.