The 2 dc you met are very young yet. It's perfectly normal for 2 yr olds not to be developmentally ready to play with other dc. At that stage, most will play alongside another child, but not with them. A 4 yr old, OTOH is massively further on with their development of social skills.
Do NOT base your decision on that conversation ! 
Having dc isn't all about the first 2 or 3 (or eve 10 or 20) years. They will be very likely to be siblings for 80 - 90 years.
The time I was most glad to have siblings, was when my parents died, toward the end of my 30s. I have no recollection of being with my siblings when I was 2, 3, or 4.
When they are still children (although older than 2) it will depend on all sorts of things, from personality, to opportunity,, to age gaps, to interests, and so forth, but, most likely there will be times they play together, times they fight, and times they either ignore each other, or just wind one another up.