New boyfriend moved in and is disrupting our whole building

I have neighbors living directly across from my apartment. Our families have known each other for decades. I grew up with their son — we went to kindergarten, school, and lived in the same building our entire lives.

About six years ago, the father passed away. A few months ago, the widow’s new, significantly younger boyfriend moved in with her. Since he arrived, the situation in the building has changed a lot.

He started renovating their apartment, but instead of doing the work during reasonable hours, he spends entire weekends drilling, hammering, breaking walls, and using heavy construction tools. The noise often lasts for hours and makes it very hard for anyone nearby to have peace and quiet.

The bigger issue, however, is how he treats the shared spaces in the building.

He has gradually started taking over the common areas as if they belong to him. He placed large planters in the hallway, removed plants and decorations that had been there for years, and replaced them with his own items without consulting anyone. He installed furniture and storage units in shared spaces and behaves as if he has full control over them.

In one case, he even threw away a decorative item belonging to my mother that had sentimental value to our family, without asking or informing us.

Additionally, I have been parking my bicycle in a shared area of the building for years with mutual understanding among the neighbors. Recently, he started placing sofas, boxes, and large bags in that same space, sometimes blocking or narrowing the passage significantly.

What frustrates me most is that a person moved into the building and began changing long-established shared spaces, removing or discarding existing items, and making decisions unilaterally without any discussion or respect for the other residents.

Has anyone dealt with a situation like this? How would you handle a neighbor who constantly makes noise on weekends and treats common building areas as if they are his private property?