Uncertainty leads to Suspense
To create suspense, the reader needs to be asking a question. They have to be guessing about ways that things could go wrong (or right!). The question could be "Is the monster going to attack the family while they eat?" or "Will the brother make enough noise to bring help?"
To generate a question like this, you need to give the reader more information than the characters. This is why people yell at the TV during horror movies - they know the "right answer" to the question, and they want the characters to pick that action.
Structure
In this case, I think you can use structure to add suspense. You can interleave sections from the monster's point of view and from the main character's point of view. Something along the lines of:
* (Monster POV) Exterior of the home. Monster must get past the dog without being attacked or generating too much barking. -- Question, will the dog save the day?
* (MC POV) Dinner Table. Quiet meal. Someone comments that the dog is quieter (or louder) than usual. 522
-- Question, will they investigate the dog? If they do, will they find anything out of the ordinary?
* (Monster POV) Interior. Monster explores the home, looking for an ambush location or isolated victim. People get up from the table to answer the doorbell, go to the bathroom, get more food from the kitchen, etc. -- Question, will any of the isolated people be attacked? Will the monster find a hiding spot?
* (MC POV) Still at dinner. Comments about brother skipping dinner to play video games / do homework / whatever. Question, will the monster discover the isolated brother!?!
* (Monster POV) Finds, stalks, and attacks brother. Question, will the brother discover the monster in time for it to matter? Can he make enough noise to bring help?
The use of the monster POV ensures that the reader has enough information to be asking questions. The uncertainty around the answers is what generates suspense. Sometimes the characters even choose the "right" answer, and the reader gets a moment of oh, everything is going to be ok - right before they are proven wrong.
So maybe the monster knocks over something in a different room, and the family investigates. It looks like the monster is going to have its cover blown, but the characters explain the noise away and go back to the meal.
For a moment, though, the reader thought they would discover the monster and they could fight it off as a group. This little release lets you build the tension back up with more questions down the road. 846