RiTEK G05 are timebomb media for a start. You will be lucky if they last a couple of months unless you somehow got a miracle batch, and even then I would not trust them.
Also, dvd's have a capacity of 4.37Gb maximum in real terms (actual bytes), and even that is pushing it unless you have primo quality media. A lot of cheaper media has serious issues toward the outside of the disk, so either test your media or be careful how much you put on it.
One other thing, the software you are using, and especially the dual process you use...can you say "worst copies ever"? If you are happy with the quality of your reshrunk 3 on 1 dvd's then I guess there's not a lot to say, but I personaly would hesitate to put three on one even with low quality vhs source.