If the apple trees are that small of diameter i would cleft graft them they will heal faster than bark grafts. Try the method i use with a butcher knife Grafting large Callery and BET pear rootstocks in 2022. I’ve got to ask how old is the current tree? Think you will say less than 10 years. If this was an old apple my opinion would change since old apples have less vigor and can die when you top work them.
2 Likes