Wenn ihr noch einen Perso / deutsche Meldeadresse habt würde ich es an eurer Stelle dann wahrscheinlich eher über eVisa beim Thai Konsulat in Deutschland machen.
Requiring a 6 months lease before even getting the visa I find rather strict and ridiculous. Sounds like a made up requirement, too, as nothing of the sort mentioned in the law.
In more legally mature countries, a non-compete clause would only be allowed in conjunction with adequate paid compensation for the duration of the clause - i.e. getting paid even after the work was terminated. That is why it isn’t all too often used in the west. No idea if Thailand had such kind of protection of the individual in mind.
It is really not often they reject a visa. In most cases, when in doubt, they just request additional / different documents and don’t just reject an application.