problematic backgrounds in my home

[Catalina]

[Colin Southern]

That greenery in the background would work pretty well. Here's one I took with a similar background:

[Catalina]

That greenery in the background would work pretty well. Here's one I took with a similar background:

What do I do to take pictures inside the house, where there is big glasses windows, and also, there are paintings and a lot and decorative objects (for example the marble head).
The extended family gathers here about 6or 7 times per year, celebrating birthdays, Christmas, etc. I want to have photos of these occasions. We gather at night, so it is easy to put the flash in front of a glass. It maybe a window, it maybe a watercolor painting.

[jcuknz]

If it is the bouncing back of the flash which concerns you you need to remember how a mirror works and if you are slightly side on to it you do not see yourself ... likewise if you are at an angle to the window the flash will be reflected past you.
[I added a cloned out date version of your photo after you saw it and commented]
The other solution is to draw the curtains.
A more complicated solution is to get a flash and direct it at the ceiling* ... here you will find YongNUo flashes have a built in 'optical sensor' which means the camera on-board flash will trigger it in synchronisation for the camera shutter. Since you are probably using a DSLR the moment you organise the on-board flash the camera will adjust the shutter speed to something appropriate for flash [ without getting into technical details ] This is roughly how I shot a family group last time I visited my son ... he has a nice white ceiling to help in this.
*he has a tripod so I mounted the flash on the tripod ... I forget what the camera was sitting on ... but using the ten second delay exposure I was able to be in the shot too. I was using his bridge camera for the shots and it blinks at you during the countdown so everybody knows when the photo will be taken.

[Colin Southern]

If you have large windows then they should be a great light source -- so position them near to a window, but not with direct sunlight falling on them. Flashes are great for fill light, but it's hard for me to give more specific advice without knowing more about the equipment that you have.

This is one I shot of my Mum in window light with some fill light from some flashes in a softbox: