query about connection of 2 relative clauses

The use of comma before the conjunction 'and' is indeed a tricky one. The thumb rule is that you use a comma before 'and' in the following two cases.
1. In a list, when there are more than two times, then we use a comma before the last ‘and’, which marks the end of the list. This is a must. However, if the list contains only two items then there is no need to put the comma.
2. (Please read carefully). A comma is used before ‘and’, when the ‘and’ joins two independent clauses, i.e., if we remove the conjunction, the two should be to stand by themselves without any crutches. In some cases, we may omit the subject for the sake of concision in the second clause in which case it is not considered independent. For example;
Tom had done his schooling in Tokyo before he had moved to Hong Kong for his collegiate education, and he returned to Tokyo to do his masters. – This is a full- fledged combination of two independent clauses joined by ‘and’, with both clauses having subjects and verbs of their own. This, therefore, needs a comma before ‘and’.
However, look at this sentence:
Tom had done his schooling in Tokyo before he had moved to Hong Kong for his collegiate education and returned to Tokyo to do his masters. – Here, the second clause is not an independent clause; it lacks a subject; in other words, for a single subject ‘Tom’ and there are two verbs. So no need to use a comma before 'and'.


Now use this thumb rule to see whether the two relative clauses are independent. Even by definition, they are relative clauses that depend upon some others and hence they are not independent. Both relative clauses are part of a list and as it was said, there is no need to use a comma when there are only two items in a list. This is as far as I know.