Are these Dear Jane blocks?
The paper pieced ones are easier.
You can blown them up, as suggested up thread, by 260%.
If you use extra big pieces on all the positions that hit the outer edges, you will able to trim down the block to 12.5" finished, without compromising the inner design.
As for the regular pieced blocks, you want to make sure that the underlying grid layout is the same.
For instance, if you have a 4.5" FINISHED 9-patch block, then each FINISHED unit its 1.5".
In a 12" FINISHED, version, that's easily enlarged to 4" FINISHED units.
Easy to cut and piece.
You don't want to end up having to deal with cutting pieces that measure 3-7/16".
So that's why the block names would be helpful.
Of course, you could use the same method as for the pp blocks.
Enlarge them, and either oversize the outer pieces, or put a little border around to get them to size so they match the other blocks.