You can sell shares that you have held.for any amount of time, either less than 12 months or greater than 12 months. The only problem with selling shares that you have held for greater than 12 months, for using to offset against capital losses, is that you will lose any CGT discount you could have claimed if you had.no losses.
In answer to the second part of your question, yes you can use small capital gains to help offset your losses amd.carry forward leftover losses to following years. After the GFC, I had carry over loses for 7 years that I gradually reduced as I made gains in following years.
