Kim,
I see that nobody has responded yet on your issues with parent-child relationships. I don't know if you still need help, but thought I would share some info on this topic using your project and hopefully I'm understanding your dilemma. I welcome others to provide input as well. I hope I don't confuse you. I apologize in advance if I do. I also apologize for the length of this post. Parent-child concept is not always the easiest no matter what the development environment is. I'll start by saying that Parent-Child record relationship does work in MVD. It's just a matter of how you want it to specifically work. Just a word of caution, it is not all automatic as one may think. Some things are automatic and others are not. Most of the time it will probably require some scripting to do exactly what you want, but not a lot and mainly minor in nature. In general terms using your parent-child scenario, you can place Table 1 and Table 2 fields on the Table 3 form, but you can only update Table 3 fields on that form using the normal MVD Save action. The other fields can only be displayed (disabled fields or set as label captions). Even if you do not disable the fields, they won't update upon save. Here are the answers to your questions.
Question 1 - Yes the parent id is stored on the child table as an integer.
Question 2 - Yes and no. I'm not exactly sure what you mean by "call all the fields from Tabone". The tabtwo.id_tabone field is only a link field with the parent id. It is typically used in a combobox on a child form and it retrieves a single text field from the parent table (in your case from Tabone). That's all it does. It does not do anything with bringing in the date field from tabone. But you can still display the date field on a child form. In your case, If you want to display the date from Table 1 onto Table 3 form, it will require a line of script.
Question 3 - Again I'm not exactly sure what you mean by "call all the fields". Probably the best way to explain how to display Table 1 and Table 2 fields on Table 3 form is to illustrate it with the following image. It is different between "ShowRecord" action and "NewRecord" action and some fields are not automatic.
The following image is a result of "ShowRecord" action from Tablegrid4 edit on Form1. No script was used for Tabthree form. Fields from Table 3 and Table 2 are shown automatically, but not Table 1 fields and the Type table text field. It requires script to retrieve that data.
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The following image is a result of "NewRecord" action from Tablegrid4 add on Form1. Again this image shows Tabthree form with no script. MVD clears all fields, including Table 2 and Table 1 fields. Therefore a script needs to be applied to bring in those fields.
The attached project mimmicks the images above except that fields are filled where necessary with script. I hope this helps. Again, if anyone else has anything to offer to help Kim in understanding this within MVD, please do so.