I've found a house that can be explored and looted (as items glow when using eagle eye (both sticks)). I've tried everything from kicking the door, ramming it and dynamite. Is there anyway into houses like this?
You can also break into certain houses by using the lock breaker. Some houses will have locked doors. When you approach them, you will get a prompt that says "break". Press Square on PS4 or X on Xbox One to use the lock breaker.
You can also get the lock breaker from any fence in the game. It'll cost you $22.50 if you get it from Seamus at Emerald Ranch and $25 from any other fence.
I haven't found any doors that use the lock breaker yet, so it's not always great for getting into houses, but it's useful if you do find a locked door and want to get in silently. Also works great for locked chests.
If the house has big enough windows, you can break one by shooting it and then climb into the house.
Otherwise, the house could be part of a quest and inaccessible until later, you will probably need to identify the specific house if you want a solution.