As same to the decks against Paradox Brothers Lvl 40, using Unhappy Girl to lockdown Gate Guardian is the best way to farm Lvl 50. So this page does not have in-depth guide. Check the link above for the basics of Unhappy Girl deck.
Straight Flush is necessary. Set it before the last turn and activate in the final turn to destroy the bros' all set spell/trap cards including Widespread Ruin, which activated when you declare attack. Unless your final attack is prevented.
All jokes aside, Curse of Anubis would be one of those cards that you might use as a last resort. I have been doing fine without it, I only use 3 Enchanted Javelin, 1 Windstorm of Etaqua and 1 E-Con. If you have no better cards, CoA is a good replacement.
Yes trap jammer is better than straight flush.
Trap jammer is a counter trap card, so you can counter it just with another counter trap card. And widespread ruin is just a normal trap card. Your final blow would be succesful .
Trap Jammer is the best choice if you have game with 1 attack (i.e. Union Attack, Gift of the Martyr), if you need multiple attacks, I would go with deckout and/or burn since having a consistent win would be harder to achieve.
spawn rate for level 50 is so low. only seen level 50 3 times and i have 8 million points lol.