I'm a firm believer in things coming up for a reason
There are extra costs with insurance and food to consider, the likelyhood of a vets visit doubles... They may not always get on and your existing dog might not want to share you and his house training may go backwards too if you say these pups aren't house trained... OTH they could be firm friends and having two dogs running together out on walks is lovely
You will need to do seperate walks for training purposes from time to time and may find you have to be less complacent about allowing one dog to pull as two is a pain in the ****
2 here was a breeze, the third OK, 4 hard work and I now usually walk in 2 goes unless I have someone with me
You sound like you've got the flexibility to work this through so if it feels right, go for it...
Good luck and photos a must
Any reason why wait till July, that seems a long time and maybe he could go back to the groomer whilst you're on hols or go with Henry... Dogs are very adaptable and I'd want to start settling him in now rather than let him get established in his foster home and then up-root him again