I've never been able to convert MKV or OGM's. Supposed to be progs out there that will but I haven't found one (re: free) that could do the job.
Hi. ConvertX is supposed to do MKV. It's listed as one of the supported file types. OGM is not listed and I don't think it is supported. I've never used either file type so I can't tell you whether it works with MKV or not. The older avi2dvd used to do OGM I think. http://www.trustfm.net/divx/SoftwareAvi2Dvd.html
I don't use WinAVI but the homepage suggest it doesn't. It isn't listed. This one apparently does. http://sourceforge.net/projects/alltoavi/
If you are using Avi2Dvd and your files OGM/MKV files already have the subtitles on them what should you do when it asks to add subtitles?
Hello I don't know as I don't work with these types of files. You'll just have to try it one way and then another and explore.