Yes, it could have come in with the two gifted birds BUT, as I said. Marek's is airborne. If your neighbor has it you have it as it can travel 5-7 miles in the air. I mentally drew a radius 5 miles from around our farm and asked myself where it could have come from and the answer is everywhere and anywhere and everyone in that 5 mile radius has been exposed the same as our flock has been.
What you need to remember is that in a recent thread somebody posted that a vet told them that it is EVERYWHERE and virtually every flock has been exposed. The difference is in resistance, whether it be from vaccinating or from breeding.
You might consider asking your neighbor if he has any sick birds. Chances are he has.
I'm really sorry to hear that Theodore isn't doing well. Keep an eye on your girls. I had a beautiful Welsummer rooster that was just 2 years old present overnight with a completely labored breathing and blue comb. I put him down other than let him suffer. Marek's is noted for causing tumors in the lungs and heart.