Hi,
The best way to understand BGP and its process decision, throw an eye on this article:
BGP Best Path Selection Process
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094431.shtml
You can use your 2 links but with a 1:1 ratio, aka equal cost multipath. Because the two BGP neighbors are iBGP (same AS), you cannot use bgp unequal cost multipath, it's only between eBGP neighbor (AS different).
The best way to achieve your unequal path loadbalacing between your two routers perhaps using an IGP which can do that like EIGRP and rely on it.
All is detailed on this link for BGP best path selection algo.
HTH
Stephane