@Kykers
What's not clear?
The Law on Foreigners in Bulgaria has an entire section on highly qualified employed, or EU Blue Card.
https://www.mig.government.bg/wp-content/uploads/2022/11/foreigners_in_the_republic_of_bulgaria_act.pdf
And for general info, here's a link on the Blue Card for Bulgaria:
https://immigration-portal.ec.europa.eu/eu-blue-card/bulgaria_en
In terms of Family Reunification, I don't think there's any difference in the process depending on what kind of residence permit you have (as long as it's valid for at least a year). If you have one (including a Blue Card) you should be able to do family reunification. The requirements for reunification are also covered in the above law.
The family permit is issued with the same validity as your residence permit. If you have 2 years, it should be 2. If you have 5 years, you expect it to be 5.
Article 33 (in above document) covers EU Blue Card. The length of your period depends on your work contract. I don't know if this is still correct, I've read other info that says validity is usually 2 years to 5 years. Do you have your Blue Card yet? How many years is it valid for?
"A permit for prolonged stay and work of the EU Blue Card type shall be issued for a period of up to 4 years. Where the term of the relevant employment contract is shorter, the permit shall be issued for a period equal to the contract term plus three months, and may be extended where there are grounds for re-issuance thereof."
My understanding is that a family reunification permit for a spouse DOES allow working, even in Bulgaria. Here is an immigration lawyer link.
https://www.delchev-lawfirm.com/blog/expatriates-in-bulgaria/eu-blue-card-for-highly-qualified-foreign-employees/
"Residence Permit for the Members of the Family of the EU Blue Card Holder - The members of the family of the EU Blue Card holder are entitled to continuous residence permits valid for the period of the EU Blue Card if for the period of their residence they dispose of lodging, health insurance and sufficient funds to support themselves no less than the minimum monthly salary (BGN 510 for 2018). Family members are also entitled to work in Bulgaria as employees or freelancers provided that they obtain the necessary permits."