If they can see you then they will catch you stealing anyway. Friendlies should not care that you sneak or it will just create annoying situations, at least they shouldn't care when you are in wilderness territory. If you are inside their house then of course they should care
This is more or less a digression from the topic but here goes. Sneaking as a mechanic prevents anyone besides those in your party from seeing you, friendly disposition or not. The only difference between sneaking and full on invisibility, AFAIK, is sneaking gives you movement speed penalty (without speedcreeper anyway) and can be broken by entering someone's sight cone. This means if you can enter sneaking mode directly in front of a friendly, then he cannot see you which enables you to pick up everything he owns right in front of his nose. If you want to go with defining an area as "wilderness", "house", etc then all of a sudden Larian is faced with the exponentially larger workload in defining just exactly what constitutes a "wilderness" and what constitutes "this person's house". In other words, the mechanics of sneaking is now inconsistent across the map and highly dependent on the specific location and the relationship between characters. I can see how it would be annoying when you have to make tactical placement involving third party friendlies prior to a battle. But in that case Larian should probably just define the third party friendlies as temporary allies/henchmen etc whose sight cones are not taken into consideration when computing for detection. Generally though I think it's better to leave the mechanism alone and enter sneaking mode by moving your rogue away from the party.
