What version of Lighthouse are you using? To achieve half your respondents getting Q1 and half getting Q2 (which is what it sounds like you want) You would want to create a quota question with 2 cells (let's call it Q1Q2Quota). Call value one Q1quota and value 2 Q2quota and set them both to 'always qualify'. The set the parameter for checking cell membership to random. This would keep them fairly even thoughout the job and then when one hits it's total it will just default to the other one. In the most recent Lighthouse version (9.7.0) there is a great new feature just for this type of situation that lets you check cell membership using 'Least fill' which will keep them perfectly even throughout the study.
That is setting up a quota, then just add a preskip to Q1 with the logic Q1Q2Quota<>1 and set is to always skip to the next question. Then at Q2 set it as Q1Q2Quota<>2.