Hello,
I am going to take a stab at this. Your graphic seems to indicate you want to advertise the low /25 of a block to one provider ('A'), while the high /25 to another ('B'). It also then indicates you want each provider to advertise a /24 to the internet. The internet will send traffic for any address within your /24, to either A or B provider. What should provider 'A' do if it receives traffic that belongs to the high /25? You aren't advertising a route to it, so it would be dropped. You would have to get provider 'A' and 'B' to exchange your /25 routes internally so that if traffic is received for, say, your high /25 block, by provider 'A', that it would be forwarded to provider 'B', who would then forward it down your other connection. Getting two different providers to do this for you is going to be difficult and I do not believe is generally done. BGP is really all about you, the end user, making your own routing policy decisions that are advertised to the whole of the rest of the net, and is not designed for this use case here. If what you really are trying to accomplish is load balancing / link redundancy, you may be better off using a wan load balancing solution such as from mushroom networks (I am not affiliated).
