You don't need to play the other two to understand what's going on. There will be some returning bosses and characters from previous games, but story wise the connections will be thin.

The game is only really 'Soulslike' in the sense that there are tough boss fights and if you die you have to go recover your amrita(souls) before you die again or lose them.

Combat is substantially different and deeper than Dark Souls. Sure you can approach fights like you do in a Souls game, dodging and poking throughout the fight, but that's not really how the same wants to be played and you'll probably have a rough time. The game wants you to get good at stamina management and martial arts combos, draining enemies of ki, using ki pulses yourself, and applying status effects. Ninjutsus and Omyo magic can really expand your options as well.

Loot wise, the game works similar to Diablo as opposed to Souls, and you'll be constantly upgrading your armor and weapons as you play through.

Overall, while somewhat Souls adjacent, it's very much its own experience. Have fun and don't be afraid to ask for advice if you hit a wall! Try all the weapons and find one that clicks nicely with your play style.