Can a tourist visa in Thailand be converted to a married visa?

Tourist visa is the one visa it can be done.

I'm married with w2 daughter's to get a 90 day visa do I have to have 400k in my thai bank account

I believe that you will require an O Visa in place in the first instance!

It can be done. It’s a two step process. With 400,000 baht in a Thai bank in your name only that is seen as have come from overseas you apply for an in country Non O visa based on marriage to a Thai. That costs 2,000 baht. Then when that visa starts to run down (ie 30 days left) you apply for an extension of stay for a year. That costs 1,900 baht. The 400k needs to have been in your account for 2 months prior to this application. They give you an under consideration stamp for 30 days. During this time some offices require the funds to remain in your bank. Once you go back and get the remaining year stamp you can then spend the funds as you see fit. To get a further year the funds will have to be back up to 400k prior to your next application.