My advice would be to immediately adjust them to a cadance of Zupreme/9Lives once they are both adjusted enough to eat solid food according to your schedule. No dry food left out at all. The 5mo old is going to be dominant and you need to gauge who's eating and who's not.
I immediately put out food after arrival and I would say that after having lunch with the breeder, it only took my girl 20-30min to attack her wet food and eventually used her box that night.
This is also your golden opportunity to get them on your routine without getting a headbutt, nibble, or otherwise woken up at night for food because they will be stressed out and exhausted, in a new place, and likely to sleep for many hours that first day/night. Their bodies are already knocked out of rhythm and you want to control feedings tightly and start them off immediately on a regular cadence.
The schedule I'm using with my two adults and 6mo old kitten:
7-8am - Breakfast, 2.5oz adult, 3oz kitten
11:30am-12:30pm - Lunch, 1oz adult, 3.5oz kitten
5-6pm - Dinner, 1.25oz adult, 3oz kitten
8-9pm - Nightcap, 1oz adult, 3.5oz kitten
It took only 2 days before my kitten realized that when I get home from work and hear the garage there is a reason why my boys are waiting for me to the point I can hardly get the door open. It's for Meal #3 and for loving.
In order to keep all happy, added the 4th meal and reduced the portions so they are not being cheated, not starving the moment I get home from work for their dinner, and most importantly, not checking out and trying to push the kitten out from her bowl. She is teething and eating such a quantity of food for her little jaws, it takes her time and supervision is absolutely required.