Number partitioning targeting ratio of subset sums and equal size
The problem is NP-hard (assuming the numbers are represented in binary).  If you could solve your problem efficiently, you could solve the Partition problem: Partition is the special case where the minimum difference is zero (and the target ratio is 1:1).  Therefore, you should not expect any simple algorithm to be both efficient and always correct.

If you want a heuristic that gives an approximation, greedy algorithms are reasonable.  I suggest you try adapting the standard algorithms for the Partition problem.  Another approach is to use an integer linear programming solver.