I'll pitch in on this one.
1) Can aprox. 70+ acres net be leased to a competing Company Yes if your lease has expired by terms, ie past it's expiration date.
2) and could they drill? Maybe. If your interest gives Company B >50% of the minerals then they would be the operator if they wanted to.
3) Must a company have the majority of the spacing unit lease directly to them in order to drill? Yes...and no. It helps. It also helps the operator to have as close to 100% of the lease in a drilling section. But they can go it as long as they have 50% or more. BUT..what happens (in this all to common of scenario) if Company A has 40%, and Company B has 30%, and the other 30% are dead, can't be found, are holding out or have leases with random Companies? They can still go to the board and ask to move forward with drilling and may get approval, but it's rarely granted, and rarely asked for as the more one company controls the better it is for them to cover the costs of the well, and thus easier to make money. Usually Company A will cut a deal of some sort with Company B so they now have 70% together. (lots of ways this can happen, but usually they swap drilling sections where they are both active, and have another split so each will drill) BUT....many times the companies will wait for the lease cycle to expire and then try to get the others leases...or they will move on to some other area.
Title: Can more than one oil company drill in a spacing unit. Yes, but it's very rare. Usually it will be done if they are drilling to 2 separate formations (like say 3 Forks and Bakken). However to do this leases taken for both companies will have to specifically say which formation the lease is for, and that's rarely done, and the OGL is for all formations...OR if one formation was released via a "vertical pugh clause" in the prior leases.