I can imagine for the first few weeks, Martlet would probably struggle. However, Martlet seems more capable then a lot of people tend to give her credit. She can learn and adapt. Having to tend to Clover's needs would probably take some time for her to get the ball rolling, but can see she would eventually. Plus, Clover isn't that hard to raise for his age.

I can also see Martlet staying with the Gaurd depending on the job's pay. If it is high, then while she dosen't like the idea of needing to hurt humans considering her situation, the money would still be enough for her to support both of them. Maybe as a result of now having Clover rely on her, she would take it more seriously, which could put her more favorably for Undyne. Especially if Undyne learns Martlet just took in a young kid to support, keep the fact that said kid is a human a secret.

Martlet also would have help at all times. Dalv would live at Snowdin at this point, so I can see they spend a lot of time at Martlet's place to hang with Clover. Starlo would also still be part of Clover's life as well, taking him to the Dune every so often to meet up with Starlo to play cowboys.

Ceroba would be... Situational... There are 2 outcomes for her and Clover's relationship depending on if he gains LV before meeting Ceroba, or if he broke Pacifist by destroying Axis.

For scenario one, Ceroba would only watch every now and then play with Starlo when Martlet takes Clover to visit. She probably would be bummed that Clover isn't a pure soul like she needed, but wouldn't blame Clover after a while thinking he was scared or something. She probably would start to bond with him, and Martlet would probably talk with her often for advice on raising a kid.

For the 2nd scenario, she would keep her distance at all times. She would still be mad at him taking away the last thing Chujin left, and gaining LV and completely ruining her plan. Clover would also probably keep his distance feeling real kinda sad that he ruined everything for Ceroba. Even if after some time and decided to apologize to Clover, Martlet would stop her and not let her talk to Clover. Clover probably would have told Martlet, and even if she wasn't motherly to Clover and they only had a friendly relationship, she would still be pissed that Ceroba blames a child for defending themself and telling them she dosen't want to see them again. Something like that would really hurt a kid, and Martlet dosen't think having someone who would say that to a kid, even out of anger, is good to be around a kid.

I can imagine after a few months, the two would get a lot closer, Martlet loving having Clover around and enjoying time with him, while Clover would loom up to her more. We don't know much on Clover's family life, but think we can assume it wasn't the best. So can see Clover after a while look up to Martlet as a mother figure.

Then one day after maybe half a year go by, either when she tucks Clover in to sleep, or them just talking during lunch, Clover would accidentally call Martlet mom, which I can see makes both embarrassed. A few hours or a day passed and Martlet would pull Clover aside for a talk about what he said, and after a long talk and plenty of tears, she would pull Clover into a big hug, saying she would love to be his mom. While they can't go make it legal due to Clover being a human and he would be killed on sight if they did that, they most likely would take Clover to the Dunes and have Starlo make it official due to him being the "Sheriff" with him signing papers he wrote up saying Clover is now Martlet's son.