I know that many people will think UFO as extra terrestrials, but could it be that these aircrafts are actually stealth spy planes from foreign governments that are doing surveillance over US territory?

We know that the US does regular flights over foreign countries for intelligence and normally we tend to think of foreign powers as "less capable" in their military technology. I think it's quite the opposite. There's heavy investment in military tech. Could be Russian or Chinese stealth spy planes. It would make more sense that this is the case than aliens from outer space.

Stealth planes would behave this way. Dropping in an out of radar, no transmission, etc.

If you think about aliens, if they were to make it to the US, they would need some sort of advance propulsion systems in their space craft. This would likely allow their space craft to NOT fly like normal earth aircraft. Why do they need to be traveling in linear patters as this incident shows?

I think foreign military is a more likely answer to the incident.