I used the Datsport seal kit on my brothers car last winter - had no problems at all pushing them into the slot – and Tracy and Baz are great to deal with.
I'll be honest though - I don’t recall removing the old ones being any problem at all. I have a nice hook tool that I likely used to get it started (but I don’t remember for sure), and I'm sure I just pulled them out without prying on anything. It takes a little to get it started, but once you have one end out, I could just pull the rest out without an issue on my brothers 4 dr, the Memorial car and the Bronze (both 2drs) - all have been replaced.
Maybe you rubber is just a lot harder than mine were.
Love people and use things,
because the opposite never works.