Twins Sharing Irregular Gestational Sac

After a failed fresh IVF transfer followed by a canceled cycle due to thin lining, I got pregnant with a natural FET. Last week (5weeks 3 days) I was told I was pregnant with twins. They saw 2 gestational sacs and a yolk sac in each. However, the second gestational sac had an irregular shape. Though too early to tell, I had prepared myself for one twin to not be viable. This week I went in and was told that the babies…now with fetal poles and heartbeats…were in the same sac, but they’re telling me the sac is still irregular. At this point they are saying that we just have to wait and see what happens. I’ll be 38 in a few months and this is my first pregnancy ever…so the added uncertainty of what’s happening is just about more than I can stand. Any insight from those who’ve experienced something similar would be greatly appreciated.