can is often for now. - I can.... Could is often for a conditional. - I could.... If.... Be able to is often for the future. - You can/will/may/should be able to ..... soon/someday/tomorrow.

"We would be able to" can be used if another condition has to be met, IE "We would be able to go if it weren't raining" Can and could are usually interchangeable.

"Can," "could," and "be able to" all overlap. I would probably use "be able to" for a situation where I want to stress THE IMPORTANCE of someone's ability to do something versus providing GENERAL INFORMATION about that person's ability. For example, your mom has just come home from the hospital and you ask her, "Do you need any help? Do you think you WILL BE ABLE TO walk on your own now?" Or a mother comments on her son's request to go to school on his own, "I guess he SHOULD BE ABLE TO find his way to school without me."

I disagree. Can and "be able to" have the same meaning. I can wash the car. = I am able to wash the car. However, could is the subjunctive form of can. The subjunctive mood is used to talk about things that are not really happening. A sponge is necessary to wash the car. Bob has a sponge, so he can wash the car. James does not have a sponge, but he could wash the car if he had one. Bob can actually wash the car right now. James cannot actually wash the car right now.