What role does 很 play in A和B很像?
A和B很像 and A跟B很像 mean the same thing, where you make a comparison between A and B. You can also say A像B.
A和B像 is like a incomplete phrase, where you put A and B together as one unit, but not to compare with each other. In order to make it complete, you might have to engage a third party to compare with A and B, like: A和B像C. A和B像C means both A and B are similar to C.
However, A和B像 can be natural in some context. E.g

Tom: A和B一点都不像！
Jim: 不！A和B像！

Basically, when we say A和B很像, our tone is natrually put a bit emphasis on 很. So, we are clear what the speaker is trying to convey. Without it, it could be interpreted as both. As you can see from above example, even A和B像 could be natural if you put more emphasis on the word 像. But with 很, you make it a lot easier.