What is the class position of those in the informal sector?

"self-employed street vendors/hawkers"

I'm very well acquainted with such people, some are friends, some are in-laws.

I know that the competition is fierce, for the costs of establishing such a business is affordable, so many have tried to sell street-food but prices are too low and profit margins insufficient to support a family and i know that they are constantly going out of business in a fairly short time because they simply don't make ends meet. It is still a hand to mouth existence, a very insecure livelihood.

I am minded how pubs got their name...public houses...and indeed most small businesses here do operate from their home and are thrown open to the public as small eating places. A bit like living over the corner shop used to be in the past.

Urban Peasant might be a description at a wild guess because the link with the countryside and the home village is not broken even in the big cities.

Are they working class?...they work...and i'm sure most identify or have an affinity with other workers in jobs...

What social role do they have? The food is dirt cheap, cheaper than eating at home in most cases, so it keeps the subsistence costs of factory workers and other employees low for the bosses.

I know i haven't really answered the question

Marx used lumpenproletariat for any urban worker not in formal employment. But the use is extremely inconsistent because he (and especially Engels) also used it for professional criminals too (who might have subordinates etc.).

https://www.marxists.org/archive/marx/works/1852/18th-brumaire/ch05.htm

The lumpen proletariat of Paris had been organized into secret sections, each section led by Bonapartist agents, with a Bonapartist general at the head of the whole. Alongside decayed roués with dubious means of subsistence and of dubious origin, alongside ruined and adventurous offshoots of the bourgeoisie, were vagabonds, discharged soldiers, discharged jailbirds, escaped galley slaves, swindlers, mountebanks, lazzaroni,[105] pickpockets, tricksters, gamblers, maquereaux [pimps], brothel keepers, porters, literati, organ grinders, ragpickers, knife grinders, tinkers, beggars — in short, the whole indefinite, disintegrated mass, thrown hither and thither, which the French call la bohème; from this kindred element Bonaparte formed the core of the Society of December 10.

He's lumping (sorry) organ grinders, knife grinders, tinkers, porters, ragpickers - in with pickpockets and brothel keepers in that list.

If you take the job of 'porter', of which there were thousands in London at the turn of the 19th century (and from which the name of the beer comes from), then it's also equivalent to 'man and van', uber drivers, bicycle couriers etc. today more or less.

This kind of self-employment where the 'tools/capital' (car, bicycle, computer, home kitchen, phone + app) is equivalent to what a person on a salary would probably own anyway, it is generally not sensible to call this 'petit bourgeois' IMO. Most of these jobs are in fact working either for one or two regular employers but with no contract or salary and being forced to purchase their own tools out of wages, or maybe direct service work for private individuals (like window cleaning, babysitting or similar).

So really it's part of the proletariat, and Marx was doing a bit of sociological classification within the proletariat, as well as mixing it in with criminal bosses.

It would be possible for a street stall to turn into an actual petit-bourgeois business with
capital and employees, but this can also happen for higher-paid salaried employees going freelance.

Petit-lumpen proletariat seems more appropriate.... You may find the works of Asef Bayat helpful analyzes the urban poor in Iran and Egypt. Can't really remember his arguments since it's been over a decade since I read him.

The UK once had the barrow-boys and costermongers. Maybe now elevated to market traders like Del-Boy's Peckham Independent Traders

"It would be possible for a street stall to turn into an actual petit-bourgeois business with
capital and employees"

Marks and Spencers

This from Endnotes talks about the historical process of capitalism creating a racialised 'surplus' population as well - i.e. proletarianised, cut off from the land, but also cut-off from wage labour. https://libcom.org/library/limit-point-capitalist-equality-notes-toward-abolitionist-antiracism-chris-chen

Narumol Nirathron's research regarding Thai vendors may be of interest.