Twin grandsons

chero I'm afraid it's a fact of life that becoming a grandparent inevitably involves costs! You can't compromise safety by buying second-hand car seats and cots (and possibly an extra buggy, etc).
Break the news to your husband that grandkids are an expensive hobby!
Best wishes for your first sleepover!

Hi - I just peeked on Mumsnet and the 'Multiple Births' topic is full of advice on twin topics.
National Childbirth Trust have their own nearly new sales.
Are the parents' car seats not available for you to use?

At 11 months I would look at a couple of cots that long term will convert to beds. You can place their cribs from home in the empty cots.

I borrowed stuff from other grandparents and bought a few bits. The car seats were the twins own just removed from parent's car and installed in ours. We borrowed a travel cot, 2 high chairs and a buggy. We bought a cheap buggy and a 2nd hand travel cot. The travel cots were big enough for them to use until they were about 2 almost 3 years old then we bought a couple of sleeping bags with built in inflatable mattresses. They were about 9 months old when they first slept over and coped very well with it all. We on the other hand were shattered.....but loved every minute!

I bought two new travel cots for our grandchildren (both out daughters had a baby within a few months of each other). You can get them for about £35 - 40 from Toys R Us or Ikea. They're still going strong almost two years later.
Ikea high chairs are £15 so I bought those new as well.
Buggies were second hand from our local area Facebook buy and sell site. (£25)

Car seats - the biggest expense. After a lot of thought we spent about £130 for seats that will grow with the children to age 4. We could have bought them second hand for about £50 but I confess to feeling overly responsible, what would I do if anything went wrong, what if the 2nd hand ones don't fit current safety regs.

We were given all kinds of good quality toys, those baby walker things by other grandparents. As has already been said, grandchildren seem to be expensive - the little ones have so much 'kit' but they are gorgeous (and exhausting)

Thank you so much for all the replies, mush appreciated. All great advice and ideas thank you. :-)