Fitting Continental GP5000TL’s to Prime RR50 wheels

I’ve just had a very difficult time fitting Continental GP5000TL tyres to brand new Prime RR50 wheels. The first bead was difficult to fit but I managed it by hand, just. The second bead was impossible to fit by hand. The problem seemed to be that the first bead fitted sat partially in the well of the rim preventing the second bead going into the well to allow lever free fitting. My wife kindly helped me (she’s a keen cyclist who’s changed loads of tyres herself, so understood the frustration I was feeling) by holding one of the three tyre levers we ended up using. I held a second lever with one hand and used a third lever (a broad, flat Schwalbe plastic lever) to lever the bead over the rim. Each time I managed to lever another few millimetres of bead over the rim my wife advanced the lever she was using up to the Schwalbe lever. I then slid the Schwalbe lever a few millimetres towards the other lever I was holding and repeated the process. This took ages and we both slipped several times before the tyre finally went onto the rim. I tried washing liquid and water, which didn’t seem to help and then GT85, just to help to slide the levers; I was desperate! I broke one tyre lever and managed to chip (it’s very small but I know I’ve done it!) one rim on the inside. I usually just read the posts submitted by others but this is the worst experience we have ever had fitting tyres! I have read posts on particular combinations of rims and tyres and my combination is definitely difficult! I’m now looking for tips to remove the tyres when this finally (in a long long time I hope!) has to happen.