SDs be more sensitive to SM?? hoo, boy that's a real KNEE SLAPPER.
Since they are showboating with the phone and want to invade your privacy, time to give them something interesting. Let them be on the phone to the BM when you should break out a convo very loudly:

"DH what lingerie would you like me in tonight?" "The one with the lace or the sheer fabric?"
"DH, can you please cash that lottery ticket in for the [insert imaginary immense sum here] I think we should buy that yacht after all."
"Now that SDs are here, the tampons are REALLY clogging up the septic system--you think we should get the tank pumped next week?"

Be creative, use your imagination.

This is if you can't ban the phone use when at your house AND if the "MMMM HMMM, that's nice" and ignore approach doesn't work.

You're giving a teenager ammunition to annoy you.

You don't. You ignore them. If you say anything about phone calls it should be the same thing you'd say about them calling anyone else.

"Honey no phone calls in the car, it's rude," and it is. I don't care who you're talking to, it's rude to be speaking loudly in a public / small space.

"Honey we're watching TV / Talking / Reading / Whatever, here in the living room. Please take your phone call to your bedroom."

Simple manners can fix the phone call issue. We don't teach anyone to take phone calls in privet anymore.

As for posting a picture of BM, ignore.

Talks about her. "That's nice" move on.

Expect them to ramp it up for a bit just to get the same reaction out of you but if you stop then they will to because it's not fun anymore.

If it's not a good relationship with them... I would not say anything. I would have your husband lay down ground rules about calls and boundaries regarding his EX's pictures etc..

I went to my dad's house for a Christmas party for the first time in 12 years. He still lives with the woman who I babysat for, then he had an affair with. Needless to say I'm not her biggest fan.

I was telling a story with my sister at the party and mentioned my mom and she shot me a look that could kill. Sorry, but my mom doesn't get deleted from my life because I crossed the threshold of your house. Now it seems your SD's are taking this over the top and I can definitely understand how annoying it is (I get those pangs when SS says "well my mom ______"). Just try to determine if they're over doing it or if you're oversensitive. Once we do, whatever side you come down on, act on that-but give it some thought first. You would be 100% within your rights to let them know this behavior is weird, and uncomfortable for you.

Great perspective.

Talking to someone on speaker phone, with others present, is just plain rude to all parties, no matter who it is. I don't want to hear someone else's conversation and I don't to be put on speaker phone when talking with someone.

Talking to them about talking about their mom? How would that conversation go, exactly?

I know it might be annoying but I wouldn't let them know that. Just ignore, or nod, or say, "That's nice," or whatever, but they do have a mom and they are going to talk about her. If they are ramping it up just to get to you, they will eventually get bored if it's not having the desired effect.

For some reason, my SD talking about her BM just never bothered me. It gave me quite the insight on the psycho bitch.

I would interject myself into the conversation, I mean when you have it on speaker and it's in a car, it's pretty much an open invitation at that point.

SD: OMG Hi Mommiiieeee!
BM: Hi baby girl how are you!
ME: Hey there BM how's parole treating you? Have they allowed you to remove that pesky ankle monitor yet? I mean bikini season is coming up...speaking of bikini season did you ever get that popped boob fixed? I mean that can't look right.

Can you imagine how quickly those conversations would end!

I am in bitch mode lately, I would have so much fun with this.
Phone calls to BM in the car warrants the radio blasting some hard rock, AC/DC Highway to Hell song. Own that song and sing along at the top of your lungs.

I have the Cd for AC/Dc in my truck, I do this when my grandsons acted like a$$holes in the truck, this is usually when I am dropping them off at school. There's nothing more embarrassing to teenage boys, then to have your grandmother belting out a song with the radio cranked up and the window down. Believe me they learn very quickly to stop acting like jerks.

Your SD16 is trying to push your buttons, and is trying to hurt your feelings. The minute you show or say that, she has a weapon to use against you. As to the family facebook page, you need to ad a caption below the BM photo with your photo. "Out with the old, In with the new."

I tried ignoring my SS's when they would do this.... it didn't work.

So then I resorted to what Gimlet suggested -- when they would bring her up in conversation (and I knew it was to poke at me) I'd play 1000 questions. Acted really interested in what she cooked, how she cooked it, etc.... where she went, who she was with, what was she wearing... I went over the top asking questions about sheer minutiae.

SS: Mom said WE'RE buying a new car
Me: Really? What kind? What color? Did she research it? What kind of gas mileage does it get? What kind of options is she looking at? Has she checked on insurance for it? Where DOES she get her insurance? Does that include her homeowners also?

They finally figured out I made it a game and gave it up. No way no how was I going to swim with those sharks while bleeding... so I became the bigger predator.

RE: phone calls to BM, I told DH to tell his sons to "take private conversations behind closed doors". I thought it best to come from him. Kept it simple and it is an "order", not a suggestion. If they forget and DH not home, I will turn on the TV and tell the kid "hey I'm watching TV here, if you want a private conversation you need to go to your bedroom so you can hear each other". When driving in the car and felt trapped by that type of conversation, I would suddenly declare how I LOVE the song playing on the radio and crank up the volume!

RE: Any talk about BM that I found annoying? Sometimes ignore and walk away and so I didn't have to listen, or talk about something else instead.

Thankfully the SS are pretty good about listening. I never make it about being "sensitive" because kids seem to see that as a weakness. I refer to it as common courtesy and good manners, learning life skills to prepare for adulthood.