Front split - need advice on narrow hurdler and vertical shin

Hi. This Friday marks 6 months since I bought the front and middle split stretch course. I've been doing each one once per week and have greatly improved my flexibility though either type of split is still several months away.

I have some questions on the proper form for two of the front split exercises.

Narrow Hurdler

When I watch Orench, Grace & Kara do this stretch I note that their "sit bones" appear to be flat on the floor next to their ankles. I have a really hard time getting into this position. For me, my *ankle* on the bent leg doesn't have sufficient flexibility for my off-side glute to get flat on the floor. 

Coach often reminds the class to stay square. Without the support, I am leaning to the side and feel like falling over. Stretching *forward* (which I thought was the point) can't happen because I lose my balance.

1. Is it okay for me to put a block under my off-side glute to support my body?

2. Should I sit seiza more often to continue working on that ankle flexibility?

3. Are there any other suggested stretches beyond what's in the video that I can add as a supplement?

Vertical Shin

I always make sure to push my knee as close to the wall as possible to make the shin as vertical as possible. However, even after 6 months of doing this I don't feel like I'm making much progress. I feel a tremendous stretch in the quad and the hip flexor (that I hold for 3m versus the 90s in the video) but progress is almost non-existent.

1. My quads and hip flexor are clearly problematic (and yes, I do have some lower back issues). What other stretches can I add to make some progress on vertical shin?

I have an overall question regarding "sets" of stretches. The video admonishes the class to only do this once per week because otherwise we'll slow down our progress because we'll be too sore. Is it advisable to pause the video and maybe cycle through 2-3 of the stretches 3+ times before moving on to the next stretches? Will this make me too sore further slowing my progress?

Thanks for any answers.

On the Narrow Hurdler, continue to use the block until your ankle mobility improves.

Sitting in regular seiza is fine more often but no need to use the block or lift the knees outside of your dedicated stretch session.

If you have time cycling through multiple times can be beneficial. you'll know if it's the right method for you if each cycle goes deeper than the last.

I am having this same issue with ankle in the narrow hurdler. It is really really tight, and that is where I feel a very intense, limiting stretch. I am also very very very poor at all of the seiza exercises--I mean really quite bad. I am not elevating my feet in seiza, just trying to keep feet in correct position on the floor is way too challenging. My heels do not want to come together, and I feel a big effort getting them to stay together, requires very active focus and feels like muscular effort. Anything to do daily to increase this mobility? I am assuming just sitting in seiza with feet together is a good plan, but not sure if there are other things to loosen up my sad ankles. I have read that people use straps to bind the ankles together. Is this overkill, or a good way to train my ankles? Thanks!