Well to start with u can have 1 hlr and have 2 id .. then as subscription /traffic increases u can assign one of the id to another hlr without any major changes .Further more u can also assign them to mated pair
Well to start ,u have to define the hlr with 2 own point codes X & Y.Then route say numbers say 0-4 to point code X and numbers say 5-9 to point code Y using either route on dpc or using gtrc towards the point codes.