To add to what was already shared, two memberships is like being two different people. You can not combine the points for a single reservation without doing a transfer first. And, once transferred, there are rules that apply.
For example, you can't borrow transferred points for a trip. Transferred points don't play nice online during the home resort booking period because MS has to create a temporary contract to hold them....and that may mean calling to use them.
If your goal is to use all your points together, then you need to have all owners the same on both of the contracts to keep them in the same membership.