»Seid ihr am Wochenende zu Hause?« – »Ja, meistens.«
Does the above mean that they are at home most weekends, or that they are at home most of the time during the weekend?
There is room for interpretation, depending on the context:
In »correct« German the question
In this case, the answer
If the interrogator wanted to know if they use to be at home on weekends he would have asked
It’s not impossible to understand it the other way round (see @Ingmar’s answer): in this case you are assuming either that the answering person has misunderstood the question or that the question has been correctly interpreted by the answering person as a sloppy way to say ›Seid ihr an Wochenenden zu Hause?‹.
Indeed it could be interpreted like this but rather within a certain context. For example:
However, without any further context information the most plausible interpretation for the OP’s question is A): ›most of the time‹.
The former. Meistens means that they are usually (lit. most of the weekends) at home. Note that in this particular case the question usually refers to the next (coming) weekend: you wouldn't answer meistens then, which is a general reply. To indicate that you will be home most of the next weekend, use something like