The completion of these achievements really is as simple as they say.
I Love Flexing!
Train in your room, waiting for your energy to refill between bouts, repeat, you'll max out your strength. Tedious but simple. Can do it before you even leave your room if you have the patience for it.
The Final Pleasure
You'll notice a bar on the lower left of the screen. While the game runs a tan-colored bar on the left will fill. Let that fill all the way and then start tapping space bar until you 'fill up the white bar next to it. Done.
Mom needs help
Go down to the basement at the start of the game. You'll find her in there and can proceed.
A Brutal Slap
This one you may be able to do without training, but I trained to max before I ever went down so someone else may wanna verify. But you just hold the mouse-button over her cheek for awhile and it should go off once the hand icon fills completely.

There, those are the simple and easy ones out of the way. Next comes the scavenger hunt.

Here, I am going to detail the items I used and where you should be able to find them in order to achieve Stretched! and Gaped!, as well as to achieve the "find these specific item" achievements.




Soon as you use your first 'fitting' item on Mom, this achievement will pop. Can't be any simpler. Be sure to use all the items on BOTH holes though to achieve both sets of stretching/gaping achievements. When you insert items you should see little hearts pop up until she's kind of 'done' with it. Once she's finished with each item, no more hearts or a prompt saying you should try something bigger comes up, even if the next achievement didn't pop, just go ahead and move on to the next item.




First, a skinny and medium sized candle. You should see them around the living area.




The white toy can be found in Dad's desk drawer. You can find his office on the second floor at the end of the hall opposite your room on the right. Face the desk from the drawer and open the drawer on the right.




The pink toy can be found in the child's room. Opposite dad's office you can find it. It is sitting in the crib.



Open the fridge and on one of the shelves you'll see the beer bottles. Just grab one. Cheers.




You should find the black toy hidden in your parents closet. On the second floor, the door opposite your bedroom leads into your parents room. You will see a sliding door into the closet. Open it and on the left, kind of tucked away in a corner behind an edge you should see it. Use it on Mom. It is the only item you SPECIFICALLY have to use. Keep this area in mind for later though.



In the kitchen area, look on the cutting board. You should see two.





The three urns can be found on a small table near the 'front' door on the right after you descend the stairs from the second floor.



It is right there in the basement. Stand by mom and look directly behind you next to what I THINK is a vacuum cleaner? You want the red one.



These are on the table near the stairs on the second floor.

With all that done, these should pop.



Now, after all that you should have only ONE achievement left. Remember how I said to keep mom's closet in mind?



Check the bottom drawer on the left side. Right on the front edge you should see it hidden. It's the only item I found after collecting everything else, so don't know 'when' you might want to include it in the order, thus my adding it here at the bottom.