Hello Pixie,
Firstly, your nephew's bloods sugar is likely to rise quite a bit higher than normal after breakfast,
due to the lack of rapid insulin. This rise can always be corrected with Novorapid.
The extra Levemir will mean that his sugars are likely to drop slightly lower than normal, particularly around mid to late afternoon. He may need slightly less rapid insulin with his lunch and evening meal because of the extra basal insulin in his system.
All the best,
timo.