I am not sure why your A1 and B1, B2 are shown in the same column in the pivot table when they are different fields in different entities. It might be helpful to understand better if you could show the relationships of these entities.
Table 3 looks like a dimension because of 1:n relationship to Table 2. At the same time it looks like a fact because you have "amount" there and you are calculating SUM. I guess your real fact table should be either Table 1 or Table 2 and you need to add some measures there. But since everything is dummy, nobody would be able to provide any suggestions. Giving proper name to 1, 2, 3 and A, B, R would make the troubleshooting easier.