the 2 new n gacha can be obtained just by buying n gacha's i got em, but they dont stack stuck at 1.21 in bonus
They do stack. You just have to level them to level 100 for their full potential. If they didn't stack, you wouldn't be able to get 1.21 (only 1.2 from 1 card). This proves that your second card is not leveled and boosts only a little.