Cat Aggressive Since Returning From Vacation - Wife Is Pregnant

My wife and I recently went to Aruba for a week. We have two cats (Max and Sookie) and a 15 month old golden doodle (Piper). Piper stayed with my in-laws while we were away, and the cats were taken care of by a neighbor.

Since we returned (3 weeks ago), Max has become aggressive. He has always been a super chill cat, until now. Mostly he is demanding attention by walking into a room and loudly meowing and coming up to be stroked. He lightly swats at me (claws not out) when I walk by him, if I don't stop to pet him. But if Piper comes near him, he will really go ballistic and chase her.

He's an indoor cat, and has never shown any interest in going outside - until now. He has escaped twice. We live at the edge of some woods, so we're more worried about coyotes and fisher cats attacking him than him running away.

We have Feliway plugged in to relax Sookie (she is very shy and sheds a lot, it helps and is preventing the vet from putting her on prozac).

The only thing I can think of that might be affecting his behaviour is the fact that my wife is pregnant (6 months). I have heard that cats change a bit.

Welcome to TCS. Did he ever get out while you were away?

No, he did discover the unfinished bonus room that wasn't properly closed when we left.. But nothing is in there (he is keen to go back in though).

Most of the day/night he is sleeping on the back of the couch, in our bed, or in his cat nest/tower. He won't always terrorize Piper, it's more frequent when my gets home from work.

I just noticed the Feliway needs to be refilled, I will replace that and see if he changes.

I am assuming that he is neutered. Have you seen any other cats around lately? That could cause him to redirect aggression toward your wife.  It also could be that the hormone changes she is going through are causing his behavior. Refilling the Feliway is a good first step. Give it a couple of days and keep us up on what is happening.