This really isn’t a Tutor problem or best place for this conversation. In a nutshell, you need to move to project-based learning and authentic assessments. Online education shifts the focus from knowledge-based to practical or application-based. The students have all of the information. Google or you give it to them. Your job is to assess if they can do something with that information. You want to know if they have transferred information to something practical, which then is evidence of their learning.
The questions that you described as problematic are incredibly valuable for the students to know if they are learning the material, but not important for you. I give my students a participation grade for completing the quizzes successfully. They can take them as many times as they want. I just count the highest grade. You have to shift your thinking from what they know (or can solve mathematically, such as calculating the feeback from an opamp or working with Kirchhoff’s laws) to what they can do giving that information. You probably have good questions for students to self-assess themselves, but you have the wrong approach to determine if they learned the material.
You can’t prevent cheating online. To minimize the opportunities, you have to create unique projects that they can’t “Google” for the answer. This requires you to rethink your methodological approach.
Give them videos to watch and opportunities for them to gain knowledge in blended learning. Then, turn your class time to interactive work or assessing their knowledge to ensure that they aren’t cheating.
I hope this helps!