A router's job is to find a subnet match in its list of routes, and forward data to that destination. It does this at the binary level. In hardware routers, there's a lookup table that has 3 types of "bits": match 0, match 1, and don't care (X). In particular the don't-care bits must be at the right-most edge and grouped.

Your first /26 is, in the router's table as a 32 bit prefix:

00001010 00000000 00000000 00XXXXXX
     (10)   (0)     (0)     (0-63 range)

The tolerable range of bits is:

00001010 00000000 00000000 00000000
   to
00001010 00000000 00000000 00111111

(When writing a subnet, you always have the don't-care bits as 0, and most software will assume that if you set any of them to 1, it's a mistake to be pointed out)

This means the subnet MUST be split along a binary point. So you 10.0.0.64 through 10.0.1.63 subnet (which is actually the size of a /24) doesn't work because the numerical range is:

00001010 00000000 00000000 01000000 (10.0.0.64)
   to
00001010 00000000 00000001 00111111 (10.0.1.63)

Can't put in "don't care" bits to get the coverage you want.