1) Use some ripping tool (e.g. DVDDecrypter, DVDFabDecrypter ...) to copy BOTH DVDs to your harddisk.
2) Use PGCDemux to demultiplex both movies to elementary streams and let it also create a chapters.txt file and a log file. (Of course, use different directories for different films!)
3) Now use IfoEdit's "Author new DVD" feature to create a DVD which will have the streams you want - that means use the video stream from the japan version, use all the audio streams from the Japan version which you WANT (skip all you don't want) and add the wished audio stream from the US version, and if you want you can also add subtitles the same way. Plese note- if the audio streams were originally multiplexed with some delay, don't forget to write the delay to the left part of the IfoEdit window, you can read the values from the log files created by PGCDemux. Also load the chapter start frames from the chapter file created by PGCDemux. When you put all your wished streams (with correct delays) to the IfoEdit authoring window, simply select a new output directory and click on Author button.
4) If you don't want menus, you are done. If you want the original menus, open in VobBlanker the DVD from which you want to take the menus (I guess it will be the american DVD). Find the PGC which represents the movie (search for the correct time if you're not sure and use the preview window) and click the Replace button on the right, in the window which appears select the movie IFO file (probably VTS_01_0.IFO) from the directory, which contains the DVD you have created in step 3 with IfoEdit. If VobBlanker throughs an error message (like new audio stream not found in the original PGC or something like that) simply click OK, we'll repair it later. Now I would recomend to go through ALL the PGCs and cells in the DVD and blank all the stuff you don't want to have on your disc, I usually do this to remove the Warning screens and trailers for other movies (or replace animated scene selection menus with still menus)and stuff like that, but this step is optional. When you're done, just select a new output directory and click Process button.
5) If VobBlanker wrote an error about audio streams in the previous step, open the newly created DVD in PGCEdit. Click OK on every message which might appear and when the scanning is finished, close the scanning window. Now search for the main movie in the left column (look for the time and use the preview window - the "`" key or the eye icon). Right click the main movie PGC and choose "Domain stream atributes". Check if all streams are listed. If some streams don't have the 2-letter language code written, write it. If you don't see your added audio stream there, but only the audio stream from the original DVD, close this window and double click the main window PGC. You will get a big window from which only the audio stream list is currently interesting for us. You should see something like a column with numbers, simply click the row under the last row with some number and with the slider select the number of the stream you have added , eg if you added your stream as third, it will have number 2 (the numbers start from 0), so select number 2. Click OK for the message and now go again to domain stream atributes. It should show you an error, just click OK and PGCDemux will fix it. Now you should have all your audio streams listed, probably you'll have to write the language code to it, if yes, do it.
Now, you can (if you want) to correct the buttons. For example if you have thrown out some of the original audio, you will probably want to hide the button which activates that language, or if you have blanked some pgcs in VobBlanker you should also remove from the menus buttons, which were leading to them. PGCEdit has a powerfull menu editor, it is activated via CTRL-M or right-clicking and selecting edit menu buttons. There are several methods how to remove a button, I recomend to hide and jump to undeleted button, or how is it called, just play with it if you want.
Save the DVD.
Wow, this section really needs screenshots, but I hope you understand what I was trying to write.
6) If the resulting DVD is too big for a standard DVD5 and you don't want to use a dual-layer DVD, open the resulting DVD in DVDShrink. When you archive the DVD, please select in the options Deep Analysis and the thing under it (adaptive error compensation ?) . This will take MUCH longer, but will give you best posible video quality.
7) Play The resulting DVD in some software player, which can read DVDs from directories - WinDVD, PowerDVD... If you didn't get some commercial DVD player to your DVD drive, you can use VideoLAN, but leave this only a your last hope, because it has some weird behaviour on some DVDs.
8) If the final DVD behavies as expected, open it in PGCEdit, and use it to create a ISO file (it's somewhere in the menu, search). When your ISO file is ready, run ISOBurn (you can also start it from PGCEdit) and burn the ISO file.
If you don't want to make the ISO file, you can burn the directory with the final DVD with Nero, but Nero is not free and ISOBurn is :-) and ISOburn is reported to have better burning results.
9) Watch the DVD on your desktop player before deleting the files from your disk !
So, this really needs screenshots, but I hope you'll understand it. If no, feel free to ask.
That were questions 1 and 2.
Question 3&5 : the answer is I DON'T KNOW, sorry. I don't even know how a laser disc looks like :-)
Question 4 : capturing from VHS - there is no general answer, it really depends on your PC and VCR. How is the VCR connected to your TV ? Is it possible to connect it the same way to your computer ? The most primitive (and cheapest) method is to buy a TV tuner, connect the VCR to your TV, connect your TV to your TV Tuner and in your capturing software try to find the VCR signal as a new chanel. It works 100%, but the results are not the best. Much better way would be to connect your VCR directly with your PC but it;s impossible for me to write which exact cables do you need, if I didn't see your hardare. But simply you have to connect video output from your VCR to the video input in your capture card (or at least a TV tuner), the same goes for audio.
Question 6 : One word only - google.
Question 7 : Of course, it's illegal. But who cares ? :-) Honestly, if you'll keep it for your self and not sell it on eBay or sth. you don't have to be afraid.
Hope that helps you.