Amazing information guys. It is very much appreciated.

It hadn't dawned on my the granted levels would count towards granting another account. I was thinking I'd just be able to pass on 30 from each of the linked accounts.

My current plan is to do the full chain and boost 4 of the accounts to 60. Then start a new party and level them up to 10.9 together. Then start the level granting at the end of the chain on to the 10.9's (always doing the lower level grants first). Here's how it should end up:

X > A > B > C > D

X - mains + 60.9 (with 15 levels left over)
A - 60 + 60.9 (with 10 levels left over)
B - 60 + 60.9
C - 60 + 40.9
D - 60 + 10.9