You cannot just "start" lineage... Did you buy your gliders from a breeder? Ask if they have proper lineage on The Pet Glider and see if you cant trace your gliders... This helps prevent inbreeding/deformities/health issues... Females are ok when getting pregnant back to back but sometimes it is good to give momma a break... my breeding pair has joeys almost every 4 months... so about 3-4 times a year... WHICH IS NORMAL...
If you do not have lineage then it is not worth breeding your glider. I do not mean to be harsh but it would not be wise to breed if they may or may not be related. It is definitely something to look into.. and if you do want to breed it is best that you buy gliders with lineage and check their COI (Coefficient Of Inbreeding) and their kinship charts to make sure they are not related in anyway and that their COI is low...
Some gliders will take a break and not want to have joeys anymore and sometimes you will buy gliders and they will pull joeys/get rid of them because they just don't want to be parents... Its all depending on a glider... you take a chance with every glider you get... they may or may not be ready for adult hood...