Can the total number of members change in Senate?

Answer 1

No, it could not be changed by Congress alone. The US Constitution would have to be amended to do so. According to Article V of the US Constitution, the process would take a vote of two thirds of both houses of Congress to propose such an amendment, or upon an application by the legislatures of two thirds of the states, it could call for a constitutional convention for the proposal of such an amendment. Once final form of the amendment has been settled upon, it would have to be ratified by three quarters of the States, in order to make such a change to the Constitution. This would result in an Amendment to the Constitution (similar to other amendments, such as the 19th Amendment, which gave women the right to vote).

Answer 2

The Constitution provides that an amendment may be proposed either by the Congress with a two-thirds majority vote in both the House of Representatives and the Senate or by a constitutional convention called for by two-thirds of the State legislatures. Article V of the Constitution.

Answer 3

No it will always be 100(2 from each state) because that is what the agreement was in the constitution.