Your question relates to the broad topic of mergers and acquisitions.
Then it specifically asks about how a deal can financed. Takeovers can be financed by cash or stock.
https://en.wikipedia.org/wiki/Mergers_and_acquisitions#Financing
No owners of B don't alway become owners of A, they might get bought out. i.e. paid a an amount in cash per share determined on a valuation in time.
