I would try to get some second hand toys or borrow some for the older ones. Maybe some Happyland style items so she has something to play. Also some puzzles and games.
My DD slept in a normal single bed at that age, you may want to think about that instead of a travel bed depending on the space where you stay. DD was still sleeping with the rails at home but because the single bed was wider she had no issues.
We're planning on visiting our family in the UK in the summer (we currently live overseas) with our 2.4 yo and new baby (should be around 6 wks). We'll be there about a month, staying with family, and I'm trying to work out what I need to arrange to borrow in advance. We're planning on taking an umbrella stroller for the older one, and a carrier/sling for the young one, and taking our own car seats. I am planning to try and borrow a moses basket/travel cot for babe, and maybe travel cot/mattress for toddler (he'll still be sleeping in a cot at home), some warm clothes and bedding for both. I can have family look out for things from NCT sales etc, if I can give them a list in advance, but what else do I need?