Multiple 5star rate up banners

Honestly don't understand what you're saying I'm just sure that you're questioning about how the said two 5 stars in the same rate up works? Yes you're right. Each five star in the same banner is .7 or even lower the more five star servant are present meaning that the more five stars the lower the chance to pull and I'm heard with three you're already rolling the story gacha which has tons of five stars. meaning the pull chance is still 1 percent, and it just increases the chances of the rate up servant from appearing meaning your monstrously lucky to get none rate up servant.

Well you are right the best chance to pull her is the Camelot 2 banner that somehow just gave me Altera after pulling her in the GSSR.

Typically multi rate ups give one servant .4 and the other .5% odds when you have two 5*s on rate up. That aside you're 100% correct this is your best chance to get her followed by the upcoming class based summoning(her and karna on rate up) and the eventual valentines event in 2 years.

If you want a good ssr lancer and not her specifically for gameplay reasons, wait in 1 or 2 month there will be class rateup banners. She share the lancer banner with karna, who are the best aoe lancer even in jp.

2 ssr on a single banner has 0.4% chance each, the remaining 0.2% chance is chance to get some other ssr that is not on rateup, divided equally to all.
On 3 or more ssr i forgot the specific percentages.