I can only respond to your post a little.

1) The body does not break down B vitamins. These occur typically in very small amounts in foods, and supplements. The supplements usually are INACTIVE forms and are chemically altered (converted to biologically active forms) after being consumed, to take part in various metabolic reactions to provide energy and tissue building the body needs.

They are water soluble and eventually excreted in the urine. If you consume a high dose of them they are therefore not all used in the tissues. If you have a genetic failure in converting them they will also be excreted in the urine as unused by the various reactions they are needed for. Today some good manufacturers will include the ACTIVE forms of B's in their products. This makes them a bit more costly. If your urine is low in B's you are either not getting enough in the diet, or using them up too quickly for the kidneys to excrete the excess.

Folic acid is inactive in the tissues and has to be metabolized in cells to methylfolate, for example. The active form of B12 is methylcobalamin (and not cyano form the inactive form which is still common in vitamin capsules).

2) B6 in vitamins is not active either, and is converted to pyridoxal 5 phosphate in the body.

You need to decide what your goals are. I have seen you on these boards for a long time. It is possible you will see some
improvement with some supplements, but there could be damage that is not fixable at this late date.

Metagenics is a prestige company-- It is very very expensive and its website is confusing and does not give the cost up front for its products. I find that deceptive in a way. On Amazon there is a price for it, at around $80.00 a bottle for the SPM.

The Methyl Guard (if the name is the same I found) is a Thorne
product and Thorne company who makes it has had a good reputation, and corresponding high priced line of supplements.
You need to decide if you want these two expensive brands.

There is solid research on using Omega products in general, however this stops short of 100%. I don't think there is HARM from them, but there may be limited effectiveness in using them.

Did you have MTHFR testing? This will show if you need Methylfolate and methycobalamin (B12) for life due to a genetic mutation which fails to convert them to activity. People with the inherited mutations are quite common (up to 40%) as this new information has recently has been explored with 23andMe and other labs advertising on TV now. The thrust of this new information is for cardiac treatment, but these two B vits are critical for many other functions in the body. This testing is not really expensive anymore and should be done if you need more complete data.

The bottom line? Neither of these 2 products are dangerous....but you may be paying way too much for these companies.