Select the newest dates sum corresponding rows up to a cumulative value in a 3rd column

I have a list of employees and I want to sum rows associate with a few values in those rows based on title and and least senior. Where this get a little more complicated is some employees are Part time (0.4, 0.53, or something less than 1 but larger than 0) and some are full time (1.00) and there are Casuals that are 0.

The calculation needs to add up liability to a cumulative FTE amount such as 7.1 of the lowest employees seniority with a specific job title.