Look:

1.هذه محامة، ينيس (This is my lawyer, Ines)----> 

lawyer= محامي   , when you make it feminine, you add ة so it becomes محامية.

and then you want to say "my lawyer" so you have to add "ي الملكية" 

ة+ي=تي    so it becomes محاميتي

هذه محاميتي ينيس

Instead of "ي", you can use "الخاصة بي" = that belongs to me 

 هذه المحامية الخاصة بي ينيس

.بنتي محامة (My daughter is a lawyer)

the same rule here: 

Son= ابن , and daughter= ابنة and to say my daughter = ابنتي

ابنتي محامية

..هم طالبون (They are students)

the rule you used for plural is correct but not for the word "طالب"

Just know that students= طلاب

The rest are correct, and hope you understood anything :)

A couple of sentences in arabic

Hi, I have a couple of new sentences and I'd appreciate if somebody could take a look at them.

.انا طالب (I'm a student)
.هذه محامة، ينيس (This is my lawyer, Ines)

.بنتي محامة (My daughter is a lawyer)
.ابني مهندس (My son is an engineer)
.اخي نيكولاس (My brother is Nicolas)
.اختي مهندسة (My sister is an engineer)

.نحن ممرضات (We are nurses)
.هم طالبون (They are students)
.هن محاسبات (They are accountants)

Para hace convertir a una palabra del masculino al femenino debemos añadir la letra ة al final de esa palabra