There are two videos here, one is older and was done about two years ago. The other is more recent. Both are good. Watch them both.
In terms of things to watch for with these stretches. Spend time in them and remember to breathe; muscles will relax if you don’t push things too far just give them time to relax. Trying to force a stretch is extremely counter productive for a couple of reasons.
1) It doesn’t actually work. Trying to force your body lower into a stretch may allow a very short immediate gain in flexibility while you grimace with pain, but this is in no way a long lasting change.
2) Forcing length into muscles is a really good way to tear them. If your body doesn’t want to go somewhere then it is likely the case because of an actual limiting factor that should be dealt with. Items like scar tissue, soft tissue damage, locked up trigger points, or a lack of strength can all be major players in limiting range of movement. These should be addressed before you try and force yourself into an oversplit.
This might mean you don’t go very deep into your stretches to start with and it might take a while to relax, but it will be worth the wait.
Note:On the whole it is usually best to start with small muscle groups and work to bigger ones, I know I do my calves after already doing my hamstrings but lets not argue about why I do that.