Air Hostess

General eligibility criterion for Air Hostess in majority of airlines is as follows:
(a) 10+2 pass from a recognised board of education. Some airlines prefer graduates.
(b) Age of candidate should be between 18 to 25 years
(c) Min height required is 157.5 centimetres and weight should be in proportion to height
(d) Good Communication skills with mastery over spoken Hindi, English. Foreign language certification will be good additional qualification.
You can become air hostess of an American Airlines which operates from India. If you want to become air hostess in an Airlines which does not operate from India, then you will require work visa I.e. H1 which no airline will sponsor under current USA president regime.

My personal suggestion would be NONE. If you think that you are a cabin crew material, please apply for all the available vacancies with the airlines. If you get selected, they train you in any case. Airlines do not trust on the training acquired from institutions. The only help you get from the institution is that of the interview dates.
In the interview, no airline will ask you any questions about Safety, First Aid or Services coz they are airline specific when it comes to service. But yes, if you are an experienced crew, be ready to answer a few technical ones. In your case they judge you on your personality, grooming, communication and BMI.
To talk about the training, Jet Airways provides one of the best training and that lasts for about 3 months.
Therefore, scrap the idea of joining a private institution to be trained on cabin crew attributes and don't waste your money.

Eligibility for Cabin Crew
-Physical requirements - Height for Air Hostesses - minimum of 157.5 cm and Flight Pursers 163 cm with proportionate weight.
-Graduates is a compulsion for international airlines in the age group of 19-25 years for training. Preference is given to Degree or Diploma holders in Hotel Management/Tourism.
-Female candidates from Home Science background, fulfilling other requirements, are also preferred. International Airlines recruit flight attendant in the age group of 18-35 years.
-Good language, ability and proficiency in English, Hindi, a regional language and at least one foreign language are essential requirements for inflight crew members working for National or International carriers.
-Normal eyesight without glasses or a minimum uncorrected distant vision of 6/40 is acceptable.
-To pursue a career as a Flight attendant, there are many institutes offering courses in Cabin crew training .
Please refer to the link for institutes offering these courses:
https://hospitality.shiksha.com/aviation-courses-in-india-categorypage-6-87-1-0-0-1-1-2-0-none-1-0?