House martin?

Hi, I'm new to this and don't know much about birds. I have had two frequent visitors to my house in the last week or so. I have noticed what seems to the start of a nest (last pic rotated 90 degrees) being built inside the porch. Are they definitely house martins? I hope so because I just bought ready made nests to place outside

Will they use a ready made nest after starting their own? I can't leave the outer door open all the time.