First of all, just know that Malaysia is one of the worst places when it comes to DTV applications. They are VERY slow request documents you already sent multiple times, and just make the entire process very complicated and and difficult.
Second, one of the required documents for a dependent DTV is the already issued DTV of the sponsor. So you must get your DTV before you can submit anyone else's application.
Given the timelines for Malaysia, and that you have to submit twice, I would expect at least 2 months total for the entire process if you do it there.
Each person needs to have their own TDAC. I don't believe the official website has any way to combine entries. It's a very short form, it won't be difficult to just submit 3 times.
You can apply for a 90 day non-O visa if you meet the requirements of your immigration office. Go there and ask them for the list. Hopefully you already have a Thai bank account since financial proof is one of the requirements. Primarily 800,000 in your Thai bank account that shows as an international transfer and has been in the account for 2 full months. The visa will have zero entries, but you can apply for a re-entry permit, single or multiple. This does make it a multiple entry visa though.
The consulates in Malaysia are known for requesting documents 2-3 times for the same thing you've already sent. You should have done better research before applying from Malaysia. It's known that you'll have to respond to MANY requests and it will likely take over a month.
TDAC is not a visa. It's just an arrival card. More than half of the fields are not even required and you can leave them blank. You can only submit TDAC within 3 days of arrival. Here's the official link:
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If for some reason you still cannot do it, you can try this agent website for TDAC. It's also free if done within 3 days of arrival, but fixes some of the UI problems.