stretching advice

When sitting on the floor legs straight out and back up in the starting position for l-sit I feel a far bit of pain build up in my sit bone and back of knees. I can't even hold the start position for l-sit for any amount of time let alone push up off the ground. Any advice on what stretching exercises would be good for me. I was thinking of one of the stretching programs on here but not shore which one would help with l-sit or other movements involving siting and or forward bending.

Tight hamstrings, they attach at sits bones and knee. Front split will help the most, middle split will help too

I'd say front split for hamstrings. My pike is already getting much better.