English for Today by Ganiu Abisoye Bamgbose (Dr GAB)

SEVERAL, MANY, SEVERALLY

I was here ~many~ times yesterday; say three to four times (nonstandard).
I was here *several* times yesterday; say three to four times (standard).
Several is used to refer to an amount that is not exact but is fewer than many; usually between three and five.

~Several~ persons were at the venue to support Hilda Bassey Effiong (nonstandard).
*Many* persons were at the venue to support Hilda Bassey Effiong (standard).
You use many to indicate that you are talking about a large number of people or things.

I came to your school *severally* (Nigerian English).
I came to your school *several times* (standard).
Note that while “severally” can be used to mean several or many times in Nigerian English (and as recognised in Online Oxford Dictionary), the word means “separately” or “individually” in other world Englishes.
I assumed the members had *severally* agreed to the condition= This means that the speaker assumed that each individual agreed.

They are jointly and *severally* (individually) responsible for the company’s debt. ✔️
GAB