When advertising for the labor certification, Could the job openig be for few numbers so that even if citizens/PRs apply, there will be room for benificiary who is appllying for Green Card. (Note: Employers need multiple people to work for that position).
For e.g. Few Senior Electrical Engineers OR Senior Electrical Engineers - 3 nos.
Will DOL accept such advt??

yes

Yes, but the advertisement must specify how many positions the company is trying to fill. I read in one reputed attorney's website that one of the cases was rejected because this information wasn't given in the advertisement. The company filled one position with US citizen and also filed for H1B for another position. Since the copy of advertisement submitted to USCIS didn't specify more than one position, the H1B was denied.

Probably, the numbers would affect the requirement for Financial Ability of Employer to sponsor the green card. Employer should have stron fincial condition.

This is the safe process where the employers have multiple hiring. Even 1 gets hired, he/she can prove that the opening is still on for others. I have seen tons of ad requesting the multiple positions available.

Recently one of the LC gets denied. And lawsuit was filed. The lawsuit got thrown out since the ad clearly states of 1 position available which was then filled by US citizen, and the alien application was rejected.