Our law firm has served many clients for inheritance in Thailand. The process for foreigners and Thai is identical and takes about 3 months in Court.
If the deceased has a Last Will and Testament or not, the process is the same. You must appoint an executor in Court and use the judgement to transfer the property of the deceased like bank accounts, cars, and immovable properties.
For more information, check https://thailawonline.com/en/family/inheritance-and-wills.html