What are the requirements and regulations for the 60-day multiple-entry Tourist Visa for Thailand?

I am looking into staying í Thailand for a few months and looking at which Visa will be best for us (me and my 14 yo). A 60 day multiple tourist Visa would be fine since we also plan to visist Cambodia and Malaysia. I know there is also a 90 day Visa but a lot more paperwork to gather.

So here are my questions for the 60 day Visa:

1. Do I understand it right that for the multientry Visa I need to book and pay for 2 tickets into Thailand and 2 tickets out of Thailand before I apply to the embassy?

2. Also it says we MAY be permitted to stay for 60 days, is that not guaranteed?

3. When is the last time I can enter if the Visa is issued on, lets say 15. August 2025 and first entry is 1. september 2025. Each stay in Thailand will be 60 days and 2-3 weeks in Cambodia and Malaysia.

Is there maybe an easier/cheaper way to do this?

TIA for your comments