Details are below
Thanks for your query.
The Recommended daily allowance of calcium is given in detail in the below link.
Recommended dietary amounts (RDAs) of Vitamin B 12 are 2.4 micrograms daily for ages 14 years and older, 2.6 micrograms daily for pregnant females, and 2.8 micrograms daily for breastfeeding
females. Those over 50 years of age should meet the RDA by eating foods reinforced with B12 or by taking a vitamin B12 supplement
. Supplementation of 25-100 micrograms daily has been used to maintain vitamin B12 levels in older people.
Yes, 3 times a week of green leafy veg in vegans is good and healthy.