RNG Distribution with multiple instances

If I need to generate random 8 bytes with RandomNumberGenerator class, I can generate all 8 bytes with a single instance and also I can use two instances of RandomNumberGenerator to generate 8 bytes - first one will generate 4 bytes and the second one will generate remaining 4 bytes. Question is - if I use two instances of RandomNumberGenerator will it make some any of 8 bytes more probable than others? Will it be a secure generator?