First take a deep breath and try to tackle each issue separately.
What is overwhelming specifically ? Is it having three kids ? Is it the small age gap ? Money worries ?
Three kids : totally appreciate this being scary and overwhelming but there's plenty of things twins can do together, they'll be going to the same school, are likely to enjoy similar things, etc. Totally different from having, say, a ten year old, a five year old and a baby.
Which brings me to the age gap. Yeah, it's harder in the early years. I don't have twins but I do have three under five and with my first two it was two under two. The first couple of years is HARD. Buuut you reap the rewards ten fold later. Mine have a wonderful relationship, play together so well, entertain each other, etc. It'll be easier in the later years as you won't be the default playmate. I think a close age gap is the best thing ever and I wish mine were closer together !
And then money. It may be a tighter fit but twins can share clothes and toys and most other things and it's possible to find cheap activities for them. You may need a bit more imagination but in some ways it's good for the kids to appreciate the value of money rather than take it for granted.
You've had a shock, take some time to breathe. You have a few months yet, you don't need to figure anything out yet. And twins are so special ! I used to hope for twins with my first two !