Two buds are definitely twins. Two buds are twins whether or not they are in the same gestational sac, and whether or not there is a clear fetal heart tube pulsation.
As long as the ultrasound clearly sees two fetal buds, it can be judged that it is twins, but whether both buds can develop normally or not, it is necessary to look at the changes of the ultrasound examination in the future, and it is possible that one of the buds will stop developing due to various factors, and it is the case that the single fetus continues to develop in the later review.
Comparatively speaking, twins will significantly increase the burden on the pregnant woman, and the chances of pregnancy complications will be significantly higher, including hypertensive disorders in pregnancy, gestational diabetes, twin-fetus transfusion syndrome, etc., so it is necessary to strengthen the monitoring, especially in the middle and late stages of pregnancy, and find abnormalities in a timely manner.