U need to miss ireland out .. get the UK visa and transfer thru london … UK visa is no good in dublin unless travelling from UK on the short stay waiver program
Going to be a challenge getting your Mrs a 6 month visa . She needs to prove there is intent to return to thailand and a reason . Ie a job
Applying for leave to enter which is path to permanent move would alternative but very expensive and not at all easy .. i assume she has not travelled much . Immigration want to see a busy passport .. an agent may be able to secure visa but not easy
If officer did not pick up on your regular visits without a visa previously u wil be ok . First time they pick up on this it will be a warning to get a visa next trip .. i had this and i know of similar other cases… there is no written rule of number of non visa entries - it is at officer discretion