On MT4, with full zoom out, each bar is 1 pixel width. And what you say about the difference of thousands of pips is right. I thing the best way to see that is as a "percent" the zero (lower of the chart) and 100 (upper of the chart) are the range. The two pairs move between that 0 and 100, and if EURUSD is at 80 and GBPUSD is at 70, then one can measure graphically the distance between the 80 and 70 percent levels on EURUSD, if that is 20 pips then that is an entry sell for EU and buy for GU. When the percent on the chart is equal, let say, 75, on both EU and GU, that is a take profit level.
For stop loss, I think it could be based on max loss on the equity, for example, I'm willing to risk only 3 percent of my account. Then, when the sum of all the open trades on EU and GU exceeds that 3 percent loss, that will signal my stop loss and I need to close all the trades.
Do you think this make sense?